Masticatory muscle tendon-aponeurosis hyperplasia exhibits heterotopic calcification in tendons.

OBJECTIVE: Masticatory muscle tendon-aponeurosis hyperplasia is a new disease entity associated with limited mouth opening. In this study, we analyzed the microstructural characteristics of muscles and tendons in masticatory muscle tendon-aponeurosis hyperplasia by electron microscopy and energy-dispersive X-ray analysis to determine the elemental composition. METHODS: Histological analysis was performed to detect the calcification. Transmission electron microscopy and scanning electron microscopy were conducted to clarify the microstructural characteristics of muscles and tendons. Energy-dispersive X-ray microanalysis was performed to identify the distribution of elements. RESULTS: Mineralized nodules were observed in tendon tissues of masticatory muscle tendon-aponeurosis hyperplasia as compared with facial deformity. Electron microscopy revealed that the muscle and tendon tissues in masticatory muscle tendon-aponeurosis hyperplasia showed degenerative changes and distinctive histological findings as compared with tissues in facial deformity. We found that Ca, P, and Si were detected only in masticatory muscle tendon-aponeurosis hyperplasia. CONCLUSION: We demonstrated that masticatory muscle tendon-aponeurosis hyperplasia exhibits heterotopic calcification in tendon tissues.

Large scale cDNA sequencing for analysis of quantitative and qualitative aspects of gene expression.

Large scale sequencing of cDNAs provides a complementary approach to structural analysis of the human genome by generating expressed sequence tags (ESTs). We have initiated the large-scale sequencing of a 3'-directed cDNA library from the human liver cell line HepG2, that is a non-biased representation of the mRNA population. 982 random cDNA clones were sequenced yielding more than 270 kilobases. A significant portion of the identified genes encoded secretable proteins and components for protein-synthesis. The abundance of cDNA species varied from 2.2% to less than 0.004%. Fifty two percent of the mRNA were abundant species consisting of 173 genes and the rest were non-abundant, consisting of about 6,600 genes.

Neurotoxic effects of methamphetamine on rat hippocampus pyramidal neurons.

Methamphetamine (MAP) is known to alter behavior and cause deficits in learning and memory. While the major site of action of MAP is on mesolimbic dopaminergic pathways, the effects on learning and memory raise the possibility of important actions in the hippocampus. We have studied electrophysiologic and morphologic effects of MAP in the CA1 region of hippocampus from young male rats chronically exposed to MAP, male rats exposed during gestation only and the effects of bath perfusion of MAP onto brain slices from control rats. Pyramidal neurons in brain slices from chronically exposed rats had reduced membrane potential and membrane resistance. Long-term potentiation (LTP) was reduced as compared to control, but when MAP was acutely perfused over control slices the amplitude of LTP was increased. LTP in young adult animals that had been gestationally exposed to MAP showed reduced LTP as compared to controls. Morphologically CA1 pyramidal neurons in chronically exposed animals showed a high prevalence of extensive blebbing of dendrites. We conclude that the NMDA receptor and the process of LTP are also targets of MAP dysfunction, at least in the hippocampus.

Pupillary autonomic dysfunction in multiple system atrophy and Parkinson's disease: an assessment by eye-drop tests.

PURPOSE: To compare pupillary autonomic dysfunction in multiple system atrophy (MSA) and Parkinson's disease (PD). METHODS: We administered eye-drop tests to 40 MSA patients, 40 PD patients with similar disease duration, and 20 age-matched healthy controls. Pupillary supersensitivity to a parasympathomimetic agent (0.05% pilocarpine hydrochloride) and to a sympathomimetic agent (0.02% dipivefrine hydrochloride) was examined by assessing changes in pupil diameter. RESULTS: Pupillary supersensitivity to a parasympathomimetic agent (0.05% pilocarpine hydrochloride) and to a sympathomimetic agent (0.02% dipivefrine hydrochloride) was examined by assessing changes in pupil diameter. Pupillary supersensitivity to 0.05% pilocarpine was greatest among the PD patients (PD -23.1 +/- 14.4%, MSA -12.4 +/- 11.5%, control -9.5 +/- 8.2%, p < 0.05) but was not correlated with disease duration. Pupillary sensitivity to 0.02% dipivefrine was significantly greater in the PD and MSA patients versus controls (PD 10.5 +/- 12.0%, MSA 11.8 +/- 11.0%, control 3.1 +/- 5.8%, p < 0.05). MSA patients had pupillary sympathetic dysfunction from an early stage, whereas in PD patients it tended to gradually accelerate as the disease advanced. In MSA patients, pupillary sympathetic sensitivity to 0.02% dipivefrine was correlated with the severity of orthostatic hypotension during a head-up tilt test and with the elevation of systolic blood pressure during a noradrenaline infusion test. In PD patients, pupillary sympathetic sensitivity to 0.02% dipivefrine was correlated with a reduction of the heart-to-mediastinum (H/M) ratio using delayed-phase iodine-123 meta-iodobenzylguanidine ((123)I-MIBG) myocardial scintigraphy. CONCLUSION: These data indicate that eye-drop tests can reveal differences in the progression of pupillary autonomic dysfunction in patients with MSA and PD.

Soft-diet feeding decreases dopamine release and impairs aversion learning in Alzheimer model rats.

To examine the effects of soft-diet feeding on the dopaminergic system in a model rat for Alzheimer's disease (AD), we measured dopamine release in the hippocampus using a microdialysis approach and assessed learning ability and memory using step-through passive avoidance tests. Furthermore, we immunohistochemically examined the ventral tegmental area (VTA), which is the origin of hippocampal dopaminergic fibers using tyrosine hydroxylase (TH), a marker enzyme for the dopaminergic nervous system. Feeding a soft diet decreased dopamine release in the hippocampus and impaired learning ability and memory in AD model rats in comparison with rats fed a hard diet; however, TH-immunopositive profiles in the VTA seemed not to be notably different between rats fed a soft diet and those fed a hard diet. These observations suggest that soft-diet feeding enhances the impairment of learning ability and memory through the decline of dopamine release in the hippocampus in AD rats.

Leptin facilitates learning and memory performance and enhances hippocampal CA1 long-term potentiation and CaMK II phosphorylation in rats.

Leptin, an adipocytokine encoded by an obesity gene and expressed in adipose tissue, affects feeding behavior, thermogenesis, and neuroendocrine status via leptin receptors distributed in the brain, especially in the hypothalamus. Leptin may also modulate the synaptic plasticity and behavioral performance related to learning and memory since: leptin receptors are found in the hippocampus, and both leptin and its receptor share structural and functional similarities with the interleukin-6 family of cytokines that modulate long-term potentiation (LTP) in the hippocampus. We therefore examined the effect of leptin on (1) behavioral performance in emotional and spatial learning tasks, (2) LTP at Schaffer collateral-CA1 synapses, (3) presynaptic and postsynaptic activities in hippocampal CA1 neurons, (4) the intracellular Ca(2+) concentration ([Ca(2+)](i)) in CA1 neurons, and (5) the activity of Ca(2+)/calmodulin protein kinase II (CaMK II) in the hippocampal CA1 tissue that exhibits LTP. Intravenous injection of 5 and/or 50mug/kg, but not of 500mug/kg leptin, facilitated behavioral performance in passive avoidance and Morris water-maze tasks. Bath application of 10(-12)M leptin in slice experiments enhanced LTP and increased the presynaptic transmitter release, whereas 10(-10)M leptin suppressed LTP and reduced the postsynaptic receptor sensitivity to N-methyl-d-aspartic acid. The increase in the [Ca(2+)](i) induced by 10(-10)M leptin was two times greater than that induced by 10(-12)M leptin. In addition, the facilitation (10(-12)M) and suppression (10(-10)M) of LTP by leptin was closely associated with an increase and decrease in Ca(2+)-independent activity of CaMK II. Our results show that leptin not only affects hypothalamic functions (such as feeding, thermogenesis, and neuroendocrine status), but also modulates higher nervous functions, such as the behavioral performance related to learning and memory and hippocampal synaptic plasticity.

Electrical characteristics of Triturus egg cells during cleavage.

The membrane potential in the blastomeres of dividing Triturus egg cells increases progressively from the first cleavage to the late morula stages. Both the animal and vegetal poles show the same increasing trend in potential; there is no significant potential difference between them. Upon first cell cleavage, the total resistance of the egg cell surface in contact with the exterior decreases to about one-tenth of its value before cleavage, and then remains rather constant up to the late morula stage. The specific resistance of this membrane surface drops rather abruptly upon first cleavage, and rises progressively during the morula stage. The resistance of the junctional membrane surface of the blastomeres, that is, the membrane formed at the former planes of cleavage, is small in relation to that of the cell surface in contact with the exterior. As a result, the blastomeres are electrically coupled throughout all stages of embryonic development examined.

Suppression of stress-induced nNOS expression in the rat hypothalamus by biting.

Nitric oxide (.NO) modulates the activity of the endocrine system in the behavioral response to stress. The purpose of this study was to investigate the effect of restraining the body of an animal on expression of neuronal nitric oxide synthase (nNOS) in the paraventricular nucleus (PVN) of the hypothalamus, and the inhibitory effect of para-masticatory activity on restraint-induced nNOS expression. We observed an increase in nNOS mRNA expression and nNOS-positive neurons in the rat hypothalamus after 30 or 60 min of restraint. Biting on a wooden stick during bodily restraint decreased nNOS mRNA expression in the hypothalamus. In addition, the number of nNOS-positive neurons was significantly reduced in the PVN of the hypothalamus. These observations clearly suggest a possible anti-stress effect of the masticatory activity of biting, and this mechanism might be unconsciously in operation during exposure to psychological stressors.

Poststreptococcal acute glomerulonephritis superimposed on bilateral renal hypoplasia.

An 8-year-old girl with preexisting chronic renal failure (CRF) due to bilateral renal hypoplasia presented with edema, gross hematuria and acute deterioration of renal function. The diagnosis of poststreptococcal acute glomerulonephritis (PSAGN) was made based on clinical presentation, red blood cell casts, low level of C3 and elevated antistreptolysin 0 titer. Her course was prolonged with serum creatinine increased from the baseline level of 1.1 mg/dl to 2.2 mg/dl, returning toward the baseline level (1.2 mg/dl) after one month. Serum creatinine then started to increase again. The slope of creatinine clearance over time became steeper after the episode of PSAGN. A severe course of PSAGN and subsequent deterioration of renal function have previously been reported in patients with diabetic nephropathy or focal glomerulosclerosis. The present case along with a literature review suggests that individuals with fewer nephrons are at higher risk of severe course and outcome of PSAGN. Conversely, patients with severe PSAGN may be born with fewer nephrons due to low birth weight, unrecognized renal hypoplasia or other unknown causes.

Eighteen novel human genes regionally mapped on chromosome 11.

Expression sequence tags (EST) obtained by sequencing a randomly primed cDNA library and gene signatures (GS) obtained by sequencing a 3'-directed cDNA library can identify genes that are active in the source cells. Eight ESTs and ten GSs which represent novel human genes, except for one GS, and which have been assigned to human chromosome 11 were used to select cosmids from a chromosome 11-specific cosmid library. These cosmids were regionally mapped using the fluorescence in situ hybridization technique.

The addition of 5'-coding information to a 3'-directed cDNA library improves analysis of gene expression.

Large-scale sequencing of a 3'-cDNA library permits one to analyse gene expression profiles in various tissues. However, many such sequences lack enough information about the encoded proteins. To overcome this problem, we tested a new library, consisting of a 3'-directed cDNA sequence fused to a to a 5' sequence of about 300 bp. Such 'joint molecules' of about 600 bp were amplified by PCR and directly sequenced. About 40% of these joint molecules included the 5' and 3' terminal portions of the mRNA, and most of the remaining clones contained the middle portion and 3' end of the mRNA. The upstream sequences contained sufficient information with which to search for similarity, ORFs, motifs and hydropathy, thus allowing the mRNAs to be categorized and their functions predicted. The rapid categorization of the cDNAs will help to sort those clones that merit further analysis.

A human cDNA sequence homologue of bovine phosphatidylethanolamine-binding protein.

Sequencing of about 1000 3'-directed cDNA clones from the human HepG2 cell line revealed that about half of them represent transcripts of abundantly or moderately expressed genes, about 70% of which are novel. We identified one of these clones as encoding the human homologue of bovine phosphatidylethanolamine-binding protein.

Inhibition of membrane-type 1 matrix metalloproteinase by hydroxamate inhibitors: an examination of the subsite pocket.

The membrane-type 1 matrix metalloproteinase (MT1-MMP) has been reported to mediate the activation of pro-gelatinase A (proMMP-2), which is associated with tumor proliferation and metastasis. MT1-MMP can also digest extracellular matrix (ECM) such as interstitial collagens, gelatin, and proteoglycan and thus may play an important role in pathophysiological digestion of ECM. We studied the inhibitory effect of various hydroxamate MMP inhibitors, including known inhibitors such as BB-94, BB-2516, GM6001, and Ro31-9790, on a deletion mutant of MT1-MMP lacking the transmembrane domain (DeltaMT1) to further characterize the enzyme and develop a selective inhibitor for MT1-MMP. The evaluation of the inhibitory activities of various hydroxamates reveals general structural profiles affecting selectivities toward MMPs. In particular, a longer side chain at the P1' position is preferable for the binding to MMP-2, -3, and -9 and MT1-MMP. For the P2' position, an alpha-branched alkyl group is critical for the binding toward DeltaMT1, while the introduction of a bulky group at the alpha-position of hydroxamic acid seems to diminish the activity against DeltaMT1. Summation of the data on the sensitivity of DeltaMT1 to various hydroxamate inhibitors indicates that (1) the volume of the S1' subsite of DeltaMT1 is similar to that of MMP-2, -3, and -9, which is bigger than that of MMP-1, and (2) the S1 and S2' subsites are narrower than those in other MMPs. On the basis of these results, the hydroxamates with a P1' phenylpropyl and P2' alpha-branched alkyl group were synthesized and evaluated for inhibitory activity. These inhibitors (1h,i) showed strong activity against DeltaMT1 over MMP-1, but no selectivity between DeltaMT1 and MMP-9. These results are explained using molecular modeling studies conducted on MT1-MMP.

Distribution of calretinin immunoreactivity in the mouse dentate gyrus: II. Mossy cells, with special reference to their dorsoventral difference in calretinin immunoreactivity.

In our previous study we revealed the presence of clustered large calretinin-immunoreactive multipolar cells in the ventral hilus of the mouse dentate gyrus and indicated that they might be mossy cells, the principal neurons in the dentate hilus. In the present study we confirmed this identification with several methods and analysed further in detail. In Golgi-impregnated samples mossy cells were easily identified by their locations and characteristic thorny excrescences on their proximal dendrites. Golgi-impregnated mossy cells were observed not only in the ventral hilus but also in the dorsal hilus, where no calretinin-immunoreactive large multipolar cells were encountered. Interestingly, mossy cells exhibited dorsoventral differences in the size and complexity of thorny excrescences; mossy cells at the dorsal and middle levels had larger and more complex thorny excrescences, which covered dendritic shafts for a longer distance, while ventral mossy cells had smaller, simpler and shorter thorny excrescences. Confocal laser scanning light microscopic observations at a high magnification showed that the vast majority of calretinin-immunoreactive large neurons in the ventral hilus displayed the thorny excrescences characteristic to mossy cells. Mossy cells identified with the intracellular injection of Lucifer Yellow were calretinin-immunoreactive. Electron microscopic observations clearly revealed that calretinin-immunoreactive elements showed structural features of mossy cells such as thorny excrescences receiving typical synapses from mossy fibre terminals. At the supragranular zone, a well-known target zone of mossy cell axons, a dense calretinin-immunoreactive band was seen, where numerous calretinin-immunoreactive punctae and fibres were packed. Electron microscopic observations revealed that these calretinin-immunoreactive axon terminals in the supragranular zone made asymmetrical synapses on presumed granule cell dendritic spines. Tracer injection studies and lesion experiments indicated that the supragranular calretinin-immunoreactive axon terminals mainly originated from the large calretinin-immunoreactive multipolar cells in the ipsilateral ventral hilus. Fluorescent double immunostaining for calretinin and glutamate receptor 2/3 (GluR2/3) revealed that all large calretinin-immunoreactive hilar cells in the ventral level were GluR2/3-immunoreactive and almost all intensely GluR2/3-immunoreactive hilar cells in the ventral level were calretinin-immunoreactive. In addition intensely GluR2/3-immunoreactive but calretinin-negative large cells were encountered in the dentate hilus at the dorsal level. On the basis of these observations, we concluded that large calretinin-immunoreactive cells in the ventral hilus of the mouse dentate gyrus were really mossy cells and that mossy cells at the dorsal level were calretinin negative. The present study revealed that mouse mossy cells show the dorsoventral difference in the calretinin immunoreactivity and thus they are chemically heterogeneous.

Failure of neuronal ion exchange, not potentiated excitation, causes excitotoxicity after inhibition of oxidative phosphorylation.

Neuronal cell death during impaired energy metabolism is often attributed to increased activity at glutamate receptors, but this increase has not been directly demonstrated. We recorded responses to glutamate and N-methyl-D-aspartate in hippocampal slice CA1 neurons and glia while inhibiting mitochondrial complex II with 3-nitropropionic acid. As the period of inhibition increased, neuronal depolarization following bath application of glutamate (5 mM) or N-methyl-D-aspartate (50 microM) increased dramatically. However, depolarization upon iontophoresis of glutamate and N-methyl-D-aspartate decreased with time. A transient hyperpolarization, reflecting electrogenic sodium pump activity, was present immediately after responses to iontophoretic glutamate agonists. In the presence of the inhibitor, this hyperpolarization decreased and eventually disappeared. Even the repolarization seen upon washing of the iontophoretic or bath application of glutamate or N-methyl-D-aspartate was incomplete. Glial depolarization upon bath application of glutamate increased during inhibition, while glial depolarization upon application of N-methyl-D-aspartate decreased. Application of the N-methyl-D-aspartate antagonists aminophosphonovaleric acid (100 microM) or MK-801 (20 microM) resulted in a delay of further depolarization when applied early during the terminal decay of membrane potential following metabolic inhibition. We conclude that during impaired oxidative phosphorylation the failure of repolarizing mechanisms, not potentiated neuronal depolarization by excitants, is the primary cause of the terminal depolarization. Large glial depolarization increases the demand for neuronal ion exchange which cannot be met in situations of reduced energy metabolism. Our results provide further evidence that acute and chronic blockade of energy metabolism have different effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Impairment of long-term potentiation and spatial memory in leptin receptor-deficient rodents.

Leptin is well known to be involved in the control of feeding, reproduction and neuroendocrine functions through its action on the hypothalamus. However, leptin receptors are found in brain regions other than the hypothalamus (including the hippocampus and cerebral cortex) suggesting extrahypothalamic functions. We investigated hippocampal long-term potentiation (LTP) and long-term depression (LTD), and the spatial-memory function in two leptin receptor-deficient rodents (Zucker rats and db/db mice). In brain slices, the CA1 hippocampal region of both strains showed impairments of LTP and LTD; leptin (10(-12) M) did not improve these impairments in either strain. These strains also showed lower basal levels of Ca(2+)/calmodulin-dependent protein kinase II activity in the CA1 region than the respective controls, and the levels did not respond to tetanic stimulation. These strains also showed impaired spatial memory in the Morris water-maze test (i.e. longer swim-path lengths during training sessions and less frequent crossings of the platform's original location in the probe test. From these results we suggest that the leptin receptor-deficient animals show impaired LTP in CA1 and poor spatial memory due, at least in part, to a deficiency in leptin receptors in the hippocampus.

Electrophysiological estimation of the actions of acetylcholinesterase inhibitors on acetylcholine receptor and cholinesterase in physically isolated Aplysia neurones.

1. The actions of representative cholinesterase inhibitors on the acetylcholine responses of physically isolated single neurones from the pedal ganglion of Aplysia californica were studied, using electrophysiological techniques and rapid agonist application to analyse both the inhibitory actions on the acetylcholine receptor-channel complex and the degree of inhibition of acetylcholinesterase activity on the same neurone. The inhibitors used were physostigmine, edrophonium and diisopropylfluorophosphate (DFP). 2. When selected neurones were suddenly exposed to 50 microM acetylcholine by a 'concentration clamp' technique a large Na-dependent inward current was initiated, and decayed in the continued presence of acetylcholine without external perfusion. However, if perfusion of the acetylcholine solution was reinitiated the current increased somewhat, indicating that the decay of current was due to some combination of receptor desensitization and local depletion of acetylcholine at the membrane by acetylcholinesterase. 3. With simultaneous application of acetylcholine (50 microM) and physostigmine (0.1 to 100 microM) there was a dose-dependent reduction of peak amplitude of the acetylcholine response. However, physostigmine at low concentrations (0.1 to 10 microM) caused a time-dependent increase in the current amplitude alone with a time- and dose-dependent inhibition of acetylcholinesterase activity. At the highest concentration of physostigmine (100 microM) acetylcholinesterase activity was abolished but the current peak was very depressed. After removal of physostigmine from the bathing solution, the current amplitude decreased toward the control at the two lower concentrations as the inhibitory actions on acetylcholinesterase activity were almost reversible, while at the two higher concentrations (10 and 100 microM) the current increased and the inhibition of acethylcholinesterase remained. 4. When acetylcholine (50 microM) and edrophonium (0.1 to 10 microM) were applied simultaneously, edrophonium caused a dose-dependent increase in the peak amplitude that was correlated with a dose-dependent inhibition of acetylcholinesterase activity. Prolonged exposure to edrophonium did not change the peak amplitude and there was no time-dependent change in the inhibition of acetylcholinesterase activity. At the highest concentration of edrophonium used (100 microM), simultaneous application with acetylcholine augmented the peak amplitude relative to control, but to a lesser extent than 10 microM. Prolonged exposure to the highest concentration of edrophonium caused a time-dependent reduction in the peak amplitude. The effects of edrophonium were quickly reversible after the removal of the drug from the bathing solution. 5. DFP (1 and 10mM), similar to 1OO microM physostigmine, caused a dramatic reduction of the peak current on simultaneous application with ftetylcholine. During exposure to DFP the current amplitude and acetylcholinesterase activity were very depressed. After removing DFP from the bathing solution the current amplitude increased to more than the control level after 1 mm DFP, while it did not recover to the control level after 10mM DFP. The inhibition of acetylcholinesterase activity remained at both concentrations. 6. These results indicate that all three cholinesterase inhibitors have dose-dependent actions both at the acetylcholine receptor-channel complex and at acetylcholinesterase. The methods we have developed may be useful in the evaluation of various cholinesterase inhibitors.

Ataxia-telangiectasia without immunodeficiency: novel point mutations within and adjacent to the phosphatidylinositol 3-kinase-like domain.

Ataxia-telangiectasia (AT) is an autosomal recessive disorder characterized by progressive ataxia, telangiectasia, sinopulmonary infections, hypersensitivity to ionizing radiation, and combined immunodeficiency. Recently, the AT gene (ATM) was cloned and shown to be mutated in AT patients. In this report, mutation analysis of ATM was performed in a 24-year-old AT patient without immunodeficiency. ATM amplified with reverse transcriptase-polymerase chain reaction (RT-PCR) was screened with a ribonuclease (RNase) cleavage assay and auto-sequenced. This patient, a compound heterozygote, showed two mutations in ATM: one missense mutation leading to a Leu2656Pro substitution and the other to the truncation at codon 3047 (Arg-->ter). The latter mutation is within the phosphatidylinositol 3-kinase (PI 3-kinase)-like domain and the former is outside but close to the domain. The particular phenotype in our patient, no immunodeficiency, suggests incomplete functional loss of ATM protein. The clinical spectrum of AT caused by ATM mutations may be broader than previously thought. Further analysis of patients with similar phenotypes will make the relation between ATM genotype and phenotype clear.

Inverted repeats in the TATA-less promoter of the rat catalase gene.

The rat catalase gene promoter lacks a TATA box, and has eight initiation sites of transcription as well as several GT and CCAAT boxes. To elucidate the mechanism of transcription in this TATA-less promoter, we analyzed nuclear factors binding to this regulatory region of the catalase gene. Functional analysis of the promoter region revealed that a pair of inverted repeat motifs located on both sides of the transcription initiation sites played an important role in the gene expression. The core sequence of this element is GYCMGGCCCKCTCYKG (M=A/C, K=G/T, Y=T/C), and four species of complex were observed to bind to this sequence. Furthermore, this element in the chimeric promoter negatively interacted with the initiator element of the terminal deoxynucleotidyl transferase gene. These results suggested that the rat catalase gene is regulated by a novel mechanism involving the inverted repeated structure of the promoter and characteristic binding factors.

Separation of protein factors that correct the defects in the seven complementation groups of xeroderma pigmentosum cells.

We fractionated HeLa cell extracts by gel filtration and then micro-injected them into cells derived from the seven complementation groups (A-G) of xeroderma pigmentosum (XP). Distinct fractions that corrected the unscheduled DNA synthesis (UDS) of the complementation group XP cells were identified. The apparent molecular weights corresponding to complementation groups A, B, C, D, E, F, and G were estimated to be 80, 600, 600, 240, 100, 240, and 280 kDa, respectively. These factors were stable in the respective cell lines, the shortest half life being 16 h for the XP-A and XP-G complementing factors. The fraction (80 kDa) that corrected the UDS in XP-A cells also complemented the defect of the XP-A cell extract in the incision of DNA containing a pyrimidine dimer in a cell-free system. The separated fractions will be useful for understanding the molecular nature of these factors and for assigning complementation groups of cells derived from suspected XP patients.