The mouse ribosomal DNA promoter has more stringent requirements in vivo than in vitro.

Using mouse ribosomal DNA templates bearing polymerase I terminators to prevent transcriptional interference (S. L. Henderson, K. Ryan, and B. Sollner-Webb, Genes Dev. 3:212-223, 1989) and facilitate promoter analysis in intact cells, we demonstrate that a -140 promoter domain (as well as the core region) is essential for appreciable levels of initiation in vivo. This in vivo polymerase I promoter can also be detected in vitro but only under very stringent conditions.

Stimulation of the mouse rRNA gene promoter by a distal spacer promoter.

We show that the mouse ribosomal DNA (rDNA) spacer promoter acts in vivo to stimulate transcription from a downstream rRNA gene promoter. This augmentation of mammalian RNA polymerase I transcription is observed in transient-transfection experiments with three different rodent cell lines, under noncompetitive as well as competitive transcription conditions, over a wide range of template concentrations, whether or not the enhancer repeats alone stimulate or repress expression from the downstream gene promoter. Stimulation of gene promoter transcription by the spacer promoter requires the rDNA enhancer sequences to be present between the spacer promoter and gene promoter and to be oriented as in native rDNA. Stimulation also requires that the spacer promoter be oriented toward the enhancer and gene promoter. However, stimulation does not correlate with transcription from the spacer promoter because the level of stimulation is not altered by either insertion of a functional mouse RNA polymerase I transcriptional terminator between the spacer promoter and enhancer or replacement with a much more active heterologous polymerase I promoter. Further analysis with a series of mutated spacer promoters indicates that the stimulatory activity does not reside in the major promoter domains but requires the central region of the promoter that has been correlated with enhancer responsiveness in vivo.

An RNA polymerase I promoter located in the CHO and mouse ribosomal DNA spacers: functional analysis and factor and sequence requirements.

We report results of experiments in which we demonstrated the existence of a polymerase I promoter within the ribosomal DNA spacer upstream from the rRNA initiation site in Chinese hamsters and mice. Transcription of the CHO spacer promoter was achieved by the same protein factors, C and D, that catalyzed transcription of the gene promoter, and these factors bound stably to the CHO spacer promoter in a preinitiation complex, just as they did to the gene promoter. In contrast to the CHO spacer promoter, which was transcribed in vitro nearly as efficiently as the gene promoter, the mouse spacer promoter was far less active; this low activity was attributable to the fact that the mouse spacer promoter bound factor D inefficiently. It is striking that the active CHO spacer promoter violated the otherwise universal rule that metazoan RNA polymerase I promoters all have a G residue at position -16. Sequence comparisons also revealed a great similarity between the CHO and mouse spacer promoter regions, yet there was much less similarity between the flanking sequences. There was also only limited homology between the spacer and gene promoter regions, but despite this the two kinds of initiation regions were organized similarly, both consisting of an essential core promoter domain and a stimulatory domain that extended upstream to approximately residue -135. Evolutionary considerations argue strongly that the presence of ribosomal DNA spacer promoters offers a significant selective advantage.

Enhancers for RNA polymerase I in mouse ribosomal DNA.

The intergenic spacer of the mouse ribosomal genes contains repetitive 140-base-pair (bp) elements which we show are enhancers for RNA polymerase I transcription analogous to the 60/81-bp repetitive enhancers (enhancers containing a 60-bp and an 81-bp element) previously characterized from Xenopus laevis. In rodent cell transfection assays, the 140-bp repeats stimulated an adjacent mouse polymerase I promoter when located in cis and competed with it when located in trans. Remarkably, in frog oocyte injection assays, the 140-bp repeats enhanced a frog ribosomal gene promoter as strongly as did the homologous 60/81-bp repeats. Mouse 140-bp repeats also competed against frog promoters in trans. The 140-bp repeats bound UBF, a DNA-binding protein we have purified from mouse extracts that is the mouse homolog of polymerase I transcription factors previously isolated from frogs and humans. The DNA-binding properties of UBF are conserved from the mouse to the frog. The same regulatory elements (terminators, gene and spacer promoters, and enhancers) have now been identified in both a mammalian and an amphibian spacer, and they are found in the same relative order. Therefore, this arrangement of elements probably is widespread in nature and has important functional consequences.

Experience with routine voluntary perinatal human immunodeficiency virus testing in an inner city hospital.

Women enrolled in prenatal care at Grady Health System, Atlanta, GA, have routinely been offered HIV counseling and voluntary testing since 1987. Consistently >90% have accepted testing. With implementation of US Public Health Service guidelines for perinatal zidovudine prophylaxis in 1994, the mother-to-child HIV transmission rate rapidly decreased from 18% to 8% during the subsequent 2 years.

Prevention of a Th1 disease by a Th1 cytokine: IL-12 and diabetes in NOD mice.

The effects of interleukin-12 on autoimmune diabetes in nonobese diabetic mice was examined. IL-12 was given, intraperitoneally, to NOD females in two different treatment protocols: three times a week, for 2 weeks beginning at 9 weeks of age and a single weekly injection, for 15 weeks, beginning at 9 weeks of age. A significant decrease in diabetes incidence was observed with multidose/short-term IL-12 treatment. Age of disease onset, however, was unchanged. Weekly administration of IL-12 was more effective in preventing onset of diabetes. Only 20% of female NOD mice become diabetic by 30 weeks of age, with a later age of onset. In spite of the decrease in diabetes incidence, no differences were seen in islet histology with treated mice compared to controls. Furthermore, IL-12 treatment of recipient mice did not prevent induction of diabetes using spleen cells from diabetic mice in adoptive transfer experiments. These observations are in contrast to reported data in which treatment of NOD mice with daily doses of IL-12 exacerbated disease incidence and hastened diabetes onset.

Acute liver failure caused by isoniazid in a child receiving carbamazepine.

We report a case of a 10-year-old boy, being treated for seizures with carbamazepine, who developed acute liver failure within four days of initiation of therapy for suspected tuberculosis with isoniazid, rifampin, pyrazinamide, and ethambutol. Isoniazid-induced liver disease was diagnosed. The likely role of carbamazepine and rifampin in potentiating the hepatotoxicity of isoniazid, and the importance of early recognition of isoniazid-induced liver disease, are discussed.

A survey of UK dental health professionals using a medicines information service: what questions do they ask and do they get useful answers?

Dentists prescribe a limited range of medicines but it is important that they consider the effects of all medicines their patients are taking when providing dental care. In the UK, a national medicines information (UKMi) service funded by the National Health Service is available to advise health professionals on prescribing and to support evidence-based practice. This paper presents the results of a survey of 151 dental health professionals who contacted the UKMi service for advice. Enquiries most commonly involved antibiotics (32%), but dental health professionals also asked for advice on legal issues relating to medicines (10%), and on managing patients receiving bisphosphonates (9%), local anaesthetics (6%) and antiplatelet drugs (5%). One hundred and forty-six (97%) enquirers used the advice provided: for managing current patients, planning the care of future patients, for continuing professional development and teaching others. Two thirds of enquirers used the information provided to check if current or proposed management was appropriate, one half to change therapy and over one quarter to identify, manage or avoid adverse effects or drug interactions.

The promoter-proximal rDNA terminator augments initiation by preventing disruption of the stable transcription complex caused by polymerase read-in.

We have examined the mechanism by which transcriptional initiation at the mouse rDNA promoter is augmented by the RNA polymerase I terminator element that resides just upstream of it. Using templates in which terminator elements are instead positioned at the opposite side of the plasmid rather than proximal to the promoter, or conditions where transcription is terminated elsewhere in the plasmid by UV-induced lesions, we show that the terminator's stimulatory effect is not position dependent. Mouse terminator elements therefore do not stimulate via the previously postulated 'read-through enhancement' model in which terminated polymerases are handed off to an adjacent promoter in a concerted reaction. The position independence and orientation dependence of the terminator also makes it unlikely that the terminator functions as a promoter element or as an enhancer. Instead, terminators serve to augment initiation by preventing polymerases from reading completely around the plasmid and through the promoter from upstream, an event which we show interferes with subsequent rounds of initiation. Notably, this transcriptional interference arises because polymerase passage across a promoter disrupts the otherwise stable transcription complex, specifically releasing the bound transcription factor D. These liberated D molecules can then bind to other templates and activate their expression. The rDNA transcriptional interference is not due to a steric impediment to the binding of new polymerase molecules, and it does not similarly liberate the initiation-competent polymerase (factor C). These studies have also convincingly demonstrated that multiple rounds of transcription are obtained from rDNA template molecules in vitro.

Increased skin pigment reduces the capacity of skin to synthesise vitamin D3.

To determine the effect of increased skin pigment on the cutaneous production of vitamin D3, circulating vitamin D concentrations were determined in two lightly pigmented Caucasian and three heavily pigmented Negro volunteers after exposure to a single standard dose of ultraviolet radiation (UVR). Exposure of Caucasian subjects to 1 minimal erythemal dose of UVR greatly increased serum vitamin-D concentrations by up to 60-fold 24-48 h after exposure, whereas this dose did not significantly change serum vitamin-D concentrations in Negro subjects. Re-exposure of one Negro subject to a dose of UVR six times larger than the standard dose increased circulating vitamin D to concentrations similar to those recorded in Caucasian subjects after exposure to the lower dose. These results indicate that increased skin pigment can greatly reduce the UVR-mediated synthesis of vitamin D.

T cell receptor alpha-chain defines the antigen specificity of antigen-specific suppressor factor but does not impart genetic restriction.

Previous studies utilizing NP (4-hydroxy, 3-nitrophenyl acetyl hapten)-specific, T suppressor hybridomas have indicated that expression of TCR-alpha, but not TCR-beta, mRNA is required for expression of Ag-specific suppressor factor bioactivity. Suppressor-effector factor has been shown to be Ag specific and I-J restricted. Although the expression of TCR-alpha mRNA was necessary for suppressor activity, the role of TCR-alpha, as it pertained to the functional properties of T cell suppressor factor (TsF), was not established. To determine which properties of TsF could be accounted for by TCR-alpha expression, TCR-alpha cDNA, derived from NP-specific, suppressor T cell (Ts) hybridomas, was transfected into recipient Ts hybridomas of a second Ag specificity. The resulting heterologous transfectants displayed NP-specific, genetically restricted TsF activity. The Ag specificity corresponded to that of the TCR-alpha donor; however, the genetic restriction was influenced by the recipient cell, implying that TCR-alpha did not control genetic restriction of the TsF. Examination of TCR-beta expression in one of the MHC-restricted transfectants indicated that the genetic restriction of TsF could not be accounted for by TCR-beta gene products. The data support the conclusion that TCR-alpha expression is not only obligate for TsF bioactivity, but that the Ag specificity of the TCR-alpha dictates the Ag specificity of the resulting suppressor factor.

The murine IL-13 receptor alpha 2: molecular cloning, characterization, and comparison with murine IL-13 receptor alpha 1.

Two components of a receptor complex for IL-13, the IL-4R and a low affinity IL-13-binding chain, IL-13R alpha 1, have been cloned in mice and humans. An additional high affinity binding chain for IL-13, IL-13R alpha 2, has been described in humans. We isolated a cDNA from the thymus that encodes the murine orthologue of the human IL-13R alpha 2. The predicted protein sequence of murine IL-13R alpha 2 (mIL-13R alpha 2) has 59% overall identity to human IL-13R alpha 2 and is closely related to the murine low affinity IL-13-binding subunit, IL-13R alpha 1. The genes for both mIL-13-binding chains map to the X chromosome. A specific interaction between mIL-13R alpha 2.Fc protein and IL-13 was demonstrated by surface plasmon resonance using a BIACORE instrument. Ba/F3 cells that were transfected with mIL-13R alpha 2 expressed 5000 molecules per cell and bound IL-13 with a single Kd of 0.5 to 1.2 nM. However, these cells did not proliferate in response to IL-13, and the IL-4 dose response was unaffected by high concentrations of IL-13. In contrast, the expression of mIL-13R alpha 1 by Ba/F3 cells resulted in a sensitive proliferative response to IL-13. Consistent with its lower affinity for IL-13, IL-13R alpha 1.Fc was 100-fold less effective than IL-13R alpha 2.Fc in neutralizing IL-13 in vitro. These results show that mIL-13R alpha 2 and mIL-13R alpha 1 are not functionally equivalent and predict distinct roles for each polypeptide in IL-13R complex formation and in the modulation of IL-13 signal transduction.

Large-scale immunoaffinity purification of recombinant soluble human antigen CD4 from Escherichia coli cells.

A large-scale immunoaffinity (IA) purification process was developed for the isolation of recombinant soluble antigen CD4 (sCD4) from Escherichia coli fermentations. The monoclonal antibody used for IA purification of sCD4 recognized a conformation-dependent epitope on the surface of domain 1 of CD4. IA chromatography was used to purify both sCD4-183, consisting of the N-terminal 183 amino acids of human CD4, and sCD4-PE40, a fusion protein consisting of the N-terminal 178 amino acids of CD4 and amino acids 1-3 and 253-613 of Pseudomonas exotoxin A (PE40). sCD4-183 was purified from E. coli cell pellets using cell disruption, protein solubilization, oxidation, Q-Sepharose anion-exchange and IA chromatography steps. sCD4-PE40 was purified from cell pellets using cell disruption, protein solubilization, oxidation, Cu(2+)-immobilized metal-affinity chromatography, anion-exchange and IA chromatography steps. The IA-purified sCD4 analogues demonstrated the correct apparent molecular masses on SDS/PAGE. The immobilized monoclonal antibody appeared to select for correctly folded CD4 protein, since sCD4-183 and sCD4-PE40 purified by the IA method bound human-immunodeficiency-virus glycoprotein gp120 (HIV gp120) in vitro. sCD4-PE40 purified by IA chromatography also inhibited protein synthesis in CV-1 cells expressing HIV gp120/160 at the cell surface. Relatively high recoveries of sCD4-183 and sCD4-PE40 were observed in the IA step of the purification process (71 and 79% recovery respectively). The results demonstrate that immobilized monoclonal antibodies directed against conformational epitopes may be used for rapid purification of gram amounts of correctly folded protein from mixtures of oxidized E. coli proteins.