The variant specific surface glycoprotein (VSG) genes of T. brucei are expressed in telomeric expression sites. We have determined the structure of the active site in trypanosome variant 221a, which contains VSG gene 221, by analysis of cloned DNA segments that represent 65 kb of the 5'-flanking region of the VSG gene. In nuclear run-on experiments, 57 kb of adjacent sequences are cotranscribed with the VSG gene at approximately similar rates and in the alpha-amanitin-resistant manner characteristic of VSG genes. Besides the VSG mRNA, this expression site yields at least seven stable RNAs, suggesting that it is a multicistronic transcription unit. Our results also show that insertion of a transcriptional terminator is not the general mechanism of switching off expression sites.
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Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA.
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From the Broad Center for Mendelian Genomics, Program in Medical and Population Genetics, Broad Institute of Massachusetts Institute of Technology and Harvard, Cambridge (V.S.G., M.C.O., J.K.G., K.V.G., E.E., B.W., F.A., D.G.M., A.O.-L.), and the Department of Neurology, Brigham and Women's Hospital (V.S.G.), the Division of Genetics and Genomics, Boston Children's Hospital (V.S.G., A.O.-L.), and Harvard Medical School (V.S.G., A.O.-L.), Boston - all in Massachusetts; L'institut du Thorax (K.R., B.I., S.B., B.C.), Service de Radiopediatrie (A.P.), and Service de Génétique Médicale (B.I., S.B., B.C.), Nantes Université, Centre Hospitalier Universitaire (CHU) de Nantes, Centre National de la Recherche Scientifique (CNRS), INSERM, Nantes, and Institut Neuromyogène, Laboratoire Physiopathologie et Génétique du Neurone et du Muscle, CNRS, INSERM (N.C., D.S.), and Service de Génétique, Hospices Civils de Lyon (N.C., P.M., D.S.), Lyon - all in France; the Departments of Neurology (E.Y., K.-M.L., M.C.A., G.L.C.) and Pharmacology (G.L.C.), Northwestern University Feinberg School of Medicine, Chicago; the Undiagnosed Diseases Network and the Department of Molecular and Human Genetics, Baylor College of Medicine, Houston (C.A.B., D.R.M., H.D., J.A.R., L.T.E., S. Ketkar), and the Department of Pediatrics, University of Texas Southwestern Medical Center (S. Kayani), and Coalition to Cure CHD2 (B.B.), Dallas; the Departments of Immunology and Regenerative Biology and Molecular Neuroscience, Weizmann Institute of Science, Rehovot, Israel (Y.S., I.U.); and the Centre for Population Genomics, Garvan Institute of Medical Research and University of New South Wales Sydney, Sydney (D.G.M.), and the Centre for Population Genomics, Murdoch Children's Research Institute, Melbourne, VIC (D.G.M.) - both in Australia.
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