La inserción académica y laboral como un factor asociado a la calidad de vida en pacientes con epilepsia farmacorresistente del lóbulo temporal / Academic and employment insertion as a factor related to quality of life in patients with drug-resistant temporal lobe epilepsy

Introducción: La inserción académica y laboral es uno de los problemas que más preocupan a las personas con epilepsia, pero permanece sin esclarecer su relación con la calidad de vida. Objetivo: Analizar los efectos de la inserción académica y laboral en la calidad de vida, la ansiedad, la depresión, el apoyo social y las funciones ejecutivas, así como la relación entre estas variables en pacientes con epilepsia farmacorresistente. Pacientes y métodos: Cincuenta y nueve pacientes con epilepsia farmacorresistente del lóbulo temporal fueron clasificados en dos grupos, con inserción académica o laboral (n = 25) y sin inserción (n = 34), y se les realizó una evaluación neuropsicológica. Resultados: Los pacientes con inserción presentaron una calidad de vida significativamente mayor, menor ansiedad rasgo y mayor apoyo social percibido, así como una tendencia a tener un menor porcentaje de errores y un mayor porcentaje de respuestas conceptuales que los pacientes sin inserción laboral. La inserción académica/laboral tuvo efectos indirectos en la calidad de vida a través de su relación con el apoyo social y la ansiedad rasgo. Conclusiones: Nuestros hallazgos ofrecen un modelo para entender la calidad de vida en los pacientes con epilepsia del lóbulo temporal desde una perspectiva integral del paciente y señalan el papel clave del aumento del apoyo social y de la reducción de la ansiedad asociados con la inserción académica y laboral para mejorar la calidad de vida. Estos resultados podrían favorecer la implementación de programas que promuevan la reinserción académica o laboral, considerando la relevancia de variables socioemocionales.(AU)

Introduction: Academic and employment insertion is one of the issues that most concern people with epilepsy, but little is known about its relationship with quality of life. Aim: We aimed to analyze the effects of the academic and employment insertion on quality of life, anxiety, depression, social support, and executive functions, and the relationships among these variables in patients with drug-resistant epilepsy. Patients and methods: Fifty-nine patients with drug-resistant temporal lobe epilepsy were classified into two groups: with academic or employment insertion (n = 25) and without insertion (n = 34) and underwent a neuropsychological evaluation. Results: Patients with insertion had a significantly better quality of life, lower trait anxiety, and higher social support, and tended to have a lower percentage of errors and higher percent conceptual level responses than those without insertion. Academic/employment insertion had indirect effects on quality of life through its relationship with global social support and trait anxiety. Conclusions: Our findings provide a model for understanding the quality of life in patients with temporal lobe epilepsy for an integral perspective of the patient and points out the key role of increased social support and reduced anxiety associated with academic and employment insertion to improve quality of life. These results could favor the implementation of programs that promote academic or employment reinsertion, considering the relevance of socio-emotional domains.(AU)

Academic and employment insertion as a factor related to quality of life in patients with drug-resistant temporal lobe epilepsy. / La inserción académica y laboral como un factor asociado a la calidad de vida en pacientes con epilepsia farmacorresistente del lóbulo temporal.

INTRODUCTION: Academic and employment insertion is one of the issues that most concern people with epilepsy, but little is known about its relationship with quality of life. AIM: We aimed to analyze the effects of the academic and employment insertion on quality of life, anxiety, depression, social support, and executive functions, and the relationships among these variables in patients with drug-resistant epilepsy. PATIENTS AND METHODS: Fifty-nine patients with drug-resistant temporal lobe epilepsy were classified into two groups: with academic or employment insertion (n = 25) and without insertion (n = 34) and underwent a neuropsychological evaluation. RESULTS: Patients with insertion had a significantly better quality of life, lower trait anxiety, and higher social support, and tended to have a lower percentage of errors and higher percent conceptual level responses than those without insertion. Academic/employment insertion had indirect effects on quality of life through its relationship with global social support and trait anxiety. CONCLUSIONS: Our findings provide a model for understanding the quality of life in patients with temporal lobe epilepsy for an integral perspective of the patient and points out the key role of increased social support and reduced anxiety associated with academic and employment insertion to improve quality of life. These results could favor the implementation of programs that promote academic or employment reinsertion, considering the relevance of socio-emotional domains.

TITLE: La inserción académica y laboral como un factor asociado a la calidad de vida en pacientes con epilepsia farmacorresistente del lóbulo temporal.Introducción. La inserción académica y laboral es uno de los problemas que más preocupan a las personas con epilepsia, pero permanece sin esclarecer su relación con la calidad de vida. Objetivo. Analizar los efectos de la inserción académica y laboral en la calidad de vida, la ansiedad, la depresión, el apoyo social y las funciones ejecutivas, así como la relación entre estas variables en pacientes con epilepsia farmacorresistente. Pacientes y métodos. Cincuenta y nueve pacientes con epilepsia farmacorresistente del lóbulo temporal fueron clasificados en dos grupos, con inserción académica o laboral (n = 25) y sin inserción (n = 34), y se les realizó una evaluación neuropsicológica. Resultados. Los pacientes con inserción presentaron una calidad de vida significativamente mayor, menor ansiedad rasgo y mayor apoyo social percibido, así como una tendencia a tener un menor porcentaje de errores y un mayor porcentaje de respuestas conceptuales que los pacientes sin inserción laboral. La inserción académica/laboral tuvo efectos indirectos en la calidad de vida a través de su relación con el apoyo social y la ansiedad rasgo. Conclusiones. Nuestros hallazgos ofrecen un modelo para entender la calidad de vida en los pacientes con epilepsia del lóbulo temporal desde una perspectiva integral del paciente y señalan el papel clave del aumento del apoyo social y de la reducción de la ansiedad asociados con la inserción académica y laboral para mejorar la calidad de vida. Estos resultados podrían favorecer la implementación de programas que promuevan la reinserción académica o laboral, considerando la relevancia de variables socioemocionales.

[Diagnostic challenges in epilepsy]. / Desafios diagnosticos en epilepsia.

INTRODUCTION: Epileptic seizures and epilepsy are part of daily clinical practice in neurology. Yet, the number of false positive diagnoses is surprisingly high. Almost one out of every five patients treated for epilepsy does not really have this diagnosis, which is a high percentage bearing in mind the social and medical consequences that being diagnosed with epilepsy entails. AIMS: To summarise the most important diagnostic challenges in epilepsy, to describe possible sources of diagnostic error and to offer advice on how to avoid them. DEVELOPMENT: Epilepsy is characterised by a tendency to suffer unprovoked epileptic seizures. The greatest obstacle when it comes to diagnosing a case of epilepsy is the fact that epileptic seizures are transient phenomena that occur relatively infrequently and the physician who must carry out the diagnosis will rarely see them. Moreover, there are other clinical events, such as syncopes or non-epileptic seizures, that may be similar to epileptic seizures in appearance and, consequently, can be mistaken for them. Finally, when interpreting the two most important complementary diagnostic techniques in epileptology, the electroencephalogram and magnetic resonance imaging of the brain, the most common errors must be taken into account in order to prevent mistaken diagnoses. CONCLUSIONS: The diagnosis of epilepsy is a challenge and must be based on a detailed and specific medical record. If there are any reasonable doubts, from the outset, about the diagnosis of epilepsy or if the patient does not respond well to the antiepileptic treatment, we recommend referring the patient to a specialised centre to establish a definitive diagnosis.

TITLE: Desafios diagnosticos en epilepsia.Introduccion. Las crisis epilepticas y la epilepsia son parte de la practica clinica diaria en neurologia. No obstante, el numero de diagnosticos falsos positivos es sorprendentemente alto. Casi uno de cada cinco pacientes tratado por epilepsia en realidad no tiene ese diagnostico, un porcentaje elevado teniendo en cuenta las consecuencias sociomedicas que conlleva el diagnostico de epilepsia. Objetivos. Resumir los desafios diagnosticos mas importantes en epilepsia, describir posibles fuentes de error en el diagnostico y proporcionar consejos sobre como evitarlos. Desarrollo. La epilepsia se caracteriza por una tendencia a sufrir crisis epilepticas no provocadas. El mayor obstaculo al diagnosticar una epilepsia radica en que las crisis epilepticas son fenomenos transitorios que ocurren relativamente con poca frecuencia y el medico que realiza el diagnostico raramente llega a verlas. Ademas, existen otros eventos clinicos, como por ejemplo sincopes o crisis no epilepticas, que pueden tener una apariencia similar a las crisis epilepticas y, en consecuencia, confundirse con ellas. Finalmente, al interpretar las dos tecnicas diagnosticas complementarias mas importantes en epileptologia, el electroencefalograma y la resonancia magnetica cerebral, deben tenerse en cuenta los errores mas comunes para prevenir diagnosticos erroneos. Conclusiones. El diagnostico de una epilepsia es un reto y debe basarse en una historia clinica detallada y especifica. Si desde el inicio existen dudas razonables sobre el diagnostico de epilepsia o si el paciente no responde bien al tratamiento antiepileptico, recomendamos derivar al paciente a un centro especializado que establezca un diagnostico definitivo.

Unravelling the mysteries of sudden unexpected death in epilepsy. / Desentrañando los misterios de la muerte súbita en epilepsia.

INTRODUCTION: Sudden unexpected death in epilepsy (SUDEP) is the most frequent cause of premature death in epileptic patients. Most SUDEP events occur at night and frequently go unnoticed; the exact pathophysiological mechanisms of this phenomenon therefore remain undetermined. Nevertheless, most cases of SUDEP are attributed to an infrequent yet extremely severe complication of epileptic seizures. DEVELOPMENT: We conducted a systematic literature search on PubMed. Our review article summarises scientific evidence on the classification, pathophysiological mechanisms, risk factors, biomarkers, and prevention of SUDEP. Likewise, we propose new lines of research and critically analyse findings that are relevant to clinical practice. CONCLUSIONS: Current knowledge suggests that SUDEP is a heterogeneous phenomenon caused by multiple factors. In most cases, however, SUDEP is thought to be due to postictal cardiorespiratory failure triggered by generalised tonic-clonic seizures and ultimately leading to cardiac arrest. The underlying pathophysiological mechanism involves multiple factors, ranging from genetic predisposition to environmental factors. Risk of SUDEP is higher in young adults with uncontrolled generalised tonic-clonic seizures. However, patients apparently at lower risk may also experience SUDEP. Current research focuses on identifying genetic and neuroimaging biomarkers that may help determine which patients are at high risk for SUDEP. Antiepileptic treatment is the only preventive measure proven effective to date. Night-time monitoring together with early resuscitation may reduce the risk of SUDEP.

Kinetics of the interaction between anti-FVIII antibodies and FVIII from therapeutic concentrates, with and without von Willebrand factor, assessed by surface plasmon resonance.

The presence of VWF in plasma-derived FVIII (pdFVIII/VWF) products has been pointed out as a key difference with recombinant FVIII (rFVIII) products with regard to immunogenicity. A Surface Plasmon Resonance (SPR) study was designed to characterize in detail the interaction between anti-FVIII (IgGs) from a severe haemophilia A patient, and FVIII from concentrates of different sources. Full-length rFVIII (preincubated or not with purified VWF), B domain-deleted (BDD)-rFVIII and pdFVIII/VWF were analysed. To ensure reproducible conditions for accurate determination of kinetic constants, a capture-based assay format was developed using protein G surfaces for specific and reversible coupling of endogenous anti-FVIII antibodies. Concentration ranges (nm) of FVIII products tested were 9-0.03 (rFVIII) and 6-0.024 (pdFVIII/VWF). The association with antibodies was monitored for 3-5 min, whereas dissociation of the complex was followed for 5-20-240 min. A strong interaction of rFVIII and BDD-rFVIII with patient's IgG was detected with the K (D) values in the low picomolar range (5.9 ± 3.0 and 12.7 ± 6.9 pm, respectively) and very slow dissociation rates, while pdFVIII/VWF showed only marginal binding signals. The VWF complexed rFVIII displayed reduced binding signals compared with uncomplexed rFVIII, but the K (D) was still in the picomolar range (4.1 ± 1.9 pm) indicating insufficient complex formation. rFVIII, alone or bound to exogenously added VWF, showed high affinity for anti-FVIII IgGs from a severe haemophilia A patient whereas pdFVIII/VWF did not. These results are in agreement with those studies that point towards rFVIII concentrates to be more immunogenic than pdFVIII concentrates.

Severe epilepsy as the major symptom of new mutations in the mitochondrial tRNA(Phe) gene.

OBJECTIVE: To present 2 families with maternally inherited severe epilepsy as the main symptom of mitochondrial disease due to point mutations at position 616 in the mitochondrial tRNA(Phe) (MT-TF) gene. METHODS: Histologic stainings were performed on skeletal muscle slices from the 2 index patients. Oxidative phosphorylation activity was measured by oxygraphic and spectrophotometric methods. The patients' complete mitochondrial DNA (mtDNA) and the relevant mtDNA region in maternal relatives were sequenced. RESULTS: Muscle histology showed only decreased overall COX staining, while a combined respiratory chain defect, most severely affecting complex IV, was noted in both patients' skeletal muscle. Sequencing of the mtDNA revealed in both patients a mutation at position 616 in the MT-TF gene (T>C or T>G). These mutations disrupt a base pair in the anticodon stem at a highly conserved position. They were apparently homoplasmic in both patients, and had different heteroplasmy levels in the investigated maternal relatives. CONCLUSIONS: Deleterious mutations in the mitochondrial tRNA(Phe) may solely manifest with epilepsy when segregating to homoplasmy. They may be overlooked in the absence of lactate accumulation and typical mosaic mitochondrial defects in muscle.

Functional involvement of G8 in the hairpin ribozyme cleavage mechanism.

The catalytic determinants for the cleavage and ligation reactions mediated by the hairpin ribozyme are integral to the polyribonucleotide chain. We describe experiments that place G8, a critical guanosine, at the active site, and point to an essential role in catalysis. Cross-linking and modeling show that formation of a catalytic complex is accompanied by a conformational change in which N1 and O6 of G8 become closely apposed to the scissile phosphodiester. UV cross-linking, hydroxyl-radical footprinting and native gel electrophoresis indicate that G8 variants inhibit the reaction at a step following domain association, and that the tertiary structure of the inactive complex is not measurably altered. Rate-pH profiles and fluorescence spectroscopy show that protonation at the N1 position of G8 is required for catalysis, and that modification of O6 can inhibit the reaction. Kinetic solvent isotope analysis suggests that two protons are transferred during the rate-limiting step, consistent with rate-limiting cleavage chemistry involving concerted deprotonation of the attacking 2'-OH and protonation of the 5'-O leaving group. We propose mechanistic models that are consistent with these data, including some that invoke a novel keto-enol tautomerization.

A base change in the catalytic core of the hairpin ribozyme perturbs function but not domain docking.

The hairpin ribozyme is a small endonucleolytic RNA motif with potential for targeted RNA inactivation. It optimally cleaves substrates containing the sequence 5'-GU-3' immediately 5' of G. Previously, we have shown that tertiary structure docking of its two domains is an essential step in the reaction pathway of the hairpin ribozyme. Here we show, combining biochemical and fluorescence structure and function probing techniques, that any mutation of the substrate base U leads to a docked RNA fold, yet decreases cleavage activity. The docked mutant complex shares with the wild-type complex a common interdomain distance as measured by time-resolved fluorescence resonance energy transfer (FRET) as well as the same solvent-inaccessible core as detected by hydroxyl-radical protection; hence, the mutant complex appears nativelike. FRET experiments also indicate that mutant docking is kinetically more complex, yet with an equilibrium shifted toward the docked conformation. Using 2-aminopurine as a site-specific fluorescent probe in place of the wild-type U, a local structural rearrangement in the substrate is observed. This substrate straining accompanies global domain docking and involves unstacking of the base and restriction of its conformational dynamics, as detected by time-resolved 2-aminopurine fluorescence spectroscopy. These data appear to invoke a mechanism of functional interference by a single base mutation, in which the ribozyme-substrate complex becomes trapped in a nativelike fold preceding the chemical transition state.

A conformational change in the "loop E-like" motif of the hairpin ribozyme is coincidental with domain docking and is essential for catalysis.

The catalysis of site-specific RNA cleavage and ligation by the hairpin ribozyme requires the formation of a tertiary interaction between two independently folded internal loop domains, A and B. Within the B domain, a tertiary structure has been identified, known as the loop E motif, that has been observed in many naturally occurring RNAs. One characteristic of this motif is a partial cross-strand stack of a G residue on a U residue. In a few cases, including loop B of the hairpin ribozyme, this unusual arrangement gives rise to photoreactivity. In the hairpin, G21 and U42 can be UV cross-linked. Here we show that docking of the two domains correlates very strongly with a loss of UV reactivity of these bases. The rate of the loss of photoreactivity during folding is in close agreement with the kinetics of interdomain docking as determined by hydroxyl-radical footprinting and fluorescence resonance energy transfer (FRET). Fixing the structure of the complex in the cross-linked form results in an inability of the two domains to dock and catalyze the cleavage reaction, suggesting that the conformational change is essential for catalysis.

The hairpin ribozyme substrate binding-domain: a highly constrained D-shaped conformation.

The two domains of the hairpin ribozyme-substrate complex, usually depicted as straight structural elements, must interact with one another in order to form an active conformation. Little is known about the internal geometry of the individual domains in an active docked complex. Using various crosslinking and structural approaches in conjunction with molecular modeling (constraint-satisfaction program MC-SYM), we have investigated the conformation of the substrate-binding domain in the context of the active docked ribozyme-substrate complex. The model generated by MC-SYM showed that the domain is not straight but adopts a bent conformation (D-shaped) in the docked state of the ribozyme, indicating that the two helices bounding the internal loop are closer than was previously assumed. This arrangement rationalizes the observed ability of hairpin ribozymes with a circularized substrate-binding strand to cleave a circular substrate, and provides essential information concerning the organization of the substrate in the active conformation. The internal geometry of the substrate-binding strand places G8 of the substrate-binding strand near the cleavage site, which has allowed us to predict the crucial role played by this nucleotide in the reaction chemistry.

Time-resolved hydroxyl-radical footprinting of RNA using Fe(II)-EDTA.

Chemical footprinting methods have been used extensively to probe the structures of biologically important RNAs at nucleotide resolution. One of these methods, hydroxyl-radical footprinting, has recently been employed to study the kinetics of RNA folding. Hydroxyl radicals can be generated by a number of different methods, including Fe(II)-EDTA complexes, synchrotron radiation, and peroxynitrous acid disproportionation. The latter two methods have been used for kinetic studies of RNA folding. We have taken advantage of rapid hydroxyl-radical generation by Fe(II)-EDTA-hydrogen peroxide solutions to develop a benchtop method to study folding kinetics of RNA complexes. This technique can be performed using commercially available chemicals, and can be used to accurately define RNA folding rate constants slower than 6 min(-1). Here we report the method and an example of time-resolved footprinting on the hairpin ribozyme, a small endoribonuclease and RNA ligase.

The solvent-protected core of the hairpin ribozyme-substrate complex.

The complex between the hairpin ribozyme and its substrate consists of two domains that must interact in order to form a catalytic complex, yet experimental evidence concerning the points of interaction between the two domains has been lacking. Here, we report the use of hydroxyl radical footprinting to define the interface between the two domains. Cations that support very efficient ribozyme catalysis (magnesium and cobalt(III) hexammine) lead to the formation of a docked complex that features several regions of protection, indicating a solvent-inaccessible core within the tertiary structure of the complex. Cations that are suboptimal in cleavage reactions do not produce complexes with regions of reduced solvent accessibility. Nucleotides encompassing the substrate cleavage site (c-2, a-1, g+1, and u+2) are strongly protected, suggesting their internalization into the catalytic core. Four distinct segments of the ribozyme are protected, including G11-A14, C25-C27, A38, and U42-A43. Protection of these sites is eliminated when g+1, an essential base at the cleavage site, is replaced by A. In addition, mutations which are known to decrease the fraction of docked complexes decrease or eliminate formation of a solvent-inaccessible core. Taken together, these observations demonstrate that we have identified the catalytic core of the active hairpin ribozyme-substrate complex.

Tertiary structure formation in the hairpin ribozyme monitored by fluorescence resonance energy transfer.

The complex formed by the hairpin ribozyme and its substrate consists of two independently folding domains which interact to form a catalytic structure. Fluorescence resonance energy transfer methods permit us to study reversible transitions of the complex between open and closed forms. Results indicate that docking of the domains is required for both the cleavage and ligation reactions. Docking is rate-limiting for ligation (2 min-1) but not for cleavage, where docking (0.5 min-1) precedes a rate-limiting conformational transition or slow-reaction chemistry. Strikingly, most modifications to the RNA (such as a G+1A mutation in the substrate) or reaction conditions (such as omission of divalent metal ion cofactors) which inhibit catalysis do so by preventing docking. This demonstrates directly that mutations and modifications which inhibit a step following substrate binding are not necessarily involved in catalysis. An improved kinetic description of the catalytic cycle is derived, including specific structural transitions.

Bile acid-independent bile flow is differently regulated by glucagon and secretin in humans after orthotopic liver transplantation.

The present study characterizes recovery of bile secretion after orthotopic liver transplantation (OLT) in humans with special regard to hormonal regulation of bile acid-independent bile flow by glucagon and secretin. Sixty-seven patients with an uncomplicated postoperative course were studied during the first 3 weeks after OLT to determine normalization of bile flow. A group of 7 and 10 patients, respectively, underwent a biliary stimulation test by either glucagon at days 7, 14, and 21 after OLT or by secretin at days 2, 10, and 21 after OLT. Secretin tests were similarly performed in patients with acute severe rejection during the first 10 days after OLT, while glucagon tests were performed in patients with acute allograft rejection occurring 2 weeks after OLT. Furthermore, hormone effects were studied in nontransplanted patients after cholecystectomy with indwelling biliary T tube. After OLT, bile secretory function recovered and stabilized within 14 days after surgery by reconstitution of both bile acid-dependent and -independent bile flow. Two weeks after OLT, bile secretion was comparable with nontransplanted patients after cholecystectomy. Glucagon and secretin stimulated bile acid-independent bile flow in transplanted and nontransplanted patients significantly, yet secretin choleresis, unlike glucagon choleresis, had already occurred during the first days after OLT and was unaffected by acute allograft rejection. These results allow the speculation that, in humans, glucagon and secretin exert their choleretic activity by different mechanisms and/or at different anatomical sites in the liver. Assuming that secretin acts at the bile duct cells, its secretory capacity was not altered by the transplantation procedure and during moderate or severe rejection episodes, as opposed to glucagon choleresis, which most likely originates in the hepatocytes and requires an entirely reconstituted canalicular transport system after OLT.

Gastroesophageal reflux in patients with sleep apnea syndrome.

UNLABELLED: Gastroesophageal reflux (GER) may be associated with pulmonary diseases. The aim of this study was to investigate the role of GER in patients with sleep apnea syndrome (SAS). We evaluated, therefore, in patients with SAS the occurrence of GER during simultaneous apnea monitoring, and whether GER is related to the severity of SAS. METHODS: 17 consecutive patients with proven SAS were divided into two groups according to the severity of SAS: (A) apnea index > or = 5 and < 15, n = 8; (B) apnea index > or = 15, n = 9. All patients underwent 24 hours pH-metry in the proximal and distal esophagus and simultaneous apnea monitoring during the night. RESULTS: There was a high occurrence of GER in patients with SAS, but no significant difference was found between the two groups with respect to reflux times at the distal or at the proximal esophageal site. Reflux episodes and apnea periods were not timely correlated. Most of the patients of both groups were obese. CONCLUSIONS: Patients with SAS often have GER. However, there is neither a relation of GER with the severity of SAS nor a timely association between GER- and SAS-episodes. Thus, it is unlikely that there is a direct link between GER and SAS. However, there may be factors predisposing for both diseases.

Specificity of monoclonal antibodies produced against phosphorothioate and ribo modified DNAs.

A large number of phosphorothioate DNAs and mixed ribo/deoxyribo duplexes were prepared and their immunogenicity was studied in mice. Only those polymers which were nuclease-resistant were immunogenic and in these cases monoclonal antibodies were prepared. The specificity of the antibodies was measured by direct and competitive Solid Phase Radioimmune Assay (SPRIA) and on this basis four types of antibody could be identified. Type I antibodies are specific for the immunizing polymer and show very limited crossreactivity. For example, Jel 384 binds only to poly(dsA).poly(dT); Jel 453 and 462 bind only to poly(dsG).poly(dC) and poly(dsG).poly(dm5C). Type II antibodies bind to most polymers containing the appropriate modification but will not bind to unmodified DNAs. For example, Jel 343 binds to most thio DNAs regardless of sequence; Jel 346 binds well to most ribose-containing polymers and may be a useful reagent for the detection of the 'A' family of conformations. Type III antibodies bind to most nucleic acids whether modified or not. Their specificities are similar to autoimmune antibodies. Type IV antibodies are single strand-specific such as Jel 383 which binds to poly(dT). There were no examples of antibodies which bound specifically to the immunizing DNA and the unmodified polymer. Thus, modified DNAs cannot be used to prepare sequence-specific reagents. Also, the immunogenicity of modified nucleic acids may limit their usefulness in antisense technologies.

A stable interaction between separated pyrimidine.purine tracts in circular DNA.

Pyrimidine.purine tracts are widespread in eukaryotic genomes and have the potential to form a number of unusual structures including triplexes. Two such tracts, which could form triplexes with each other but not with themselves, were cloned into a plasmid at separate sites. Upon lowering the pH, linear, open circular and relaxed plasmid molecules formed a number of novel structures that were observed on agarose gels and directly by electron microscopy. In open circles a stable join was formed between the two Pyr.Pur tracts giving rise to molecules resembling dumbells, trefoils and tetrafoils, which collectively are termed T-loops. The structure was stable at pH 8 and contains a single-stranded region that was sensitive to P1 nuclease. Thus, there is no apparent topological impediment to the formation of triplex-mediated loops in circular molecules. These structures may be important for gene regulation and chromosome condensation.

Kilobase-range communication between polypurine.polypyrimidine tracts in linear plasmids mediated by triplex formation: a braided knot between two linear duplexes.

Linear plasmids were constructed containing two pyrimidine tracts that were 0.34 and 0.94 kilobases (kb) from either end and were separated by 2.8 kb. The tracts [d(TCCTTC)n and d(CTTCCT)n where n = 6 or 12] were designed so as to be able to form triplexes with each other but not with themselves. Upon lowering of the pH to 4 in the presence of spermine, these plasmids form intermolecular dimers and intramolecular loops of 2.8 kb, as judged from mobility changes on agarose gels. A tethered loop could also be formed in a linear plasmid containing two identical tracts by adding an homologous single-stranded oligopyrimidine, but not an oligopurine. In plasmids containing different tracts, the formation of both dimers and loops could be blocked by adding either homologous single-stranded oligopyrimidine but not an oligopurine. Together with the requirement of low pH, these results demonstrate that triplex formation is of the pyr.pur.pyr type. The extent of dimer and loop formation was dependent on the length of the pyrimidine tract: dimers could be detected in plasmids containing the 72 base pair (bp) inserts after incubation at pH 6, but in plasmids containing the 36 bp inserts, a pH of 5 was required. Hysteresis was also evident to a remarkable extent. Once formed at pH 4, loops and dimers remained stable indefinitely at pH 8, suggesting that the structures become topologically trapped. However, the structures were resolved into the component linear plasmids by incubation with nuclease P1. This is the first demonstration of a braided or hydrogen-bonded knot between two linear duplexes and may have implications for chromosomal loop formation.