The DNA sequence of chromosome I of an African trypanosome: gene content,chromosome organisation,recombination and polymorphism |
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Authors: | Hall Neil Berriman Matthew Lennard Nicola J Harris Barbara R Hertz-Fowler Christiane Bart-Delabesse Emmanuelle N Gerrard Caroline S Atkin Rebecca J Barron Andrew J Bowman Sharen Bray-Allen Sarah P Bringaud Frédéric Clark Louise N Corton Craig H Cronin Ann Davies Robert Doggett Jonathon Fraser Audrey Grüter Eric Hall Sarah Harper A David Kay Mike P Leech Vanessa Mayes Rebecca Price Claire Quail Michael A Rabbinowitsch Ester Reitter Christopher Rutherford Kim Sasse Jürgen Sharp Sarah Shownkeen Ratna MacLeod Annette Taylor Sonya Tweedie Alison Turner C Michael R Tait Andrew Gull Keith |
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Institution: | The Wellcome Trust Sanger Institute, The Wellcome Trust Genome Campus, Hinxton CB10 1SA, UK. |
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Abstract: | The African trypanosome, Trypanosoma brucei, causes sleeping sickness in humans in sub-Saharan Africa. Here we report the sequence and analysis of the 1.1 Mb chromosome I, which encodes approximately 400 predicted genes organised into directional clusters, of which more than 100 are located in the largest cluster of 250 kb. A 160-kb region consists primarily of three gene families of unknown function, one of which contains a hotspot for retroelement insertion. We also identify five novel gene families. Indeed, almost 20% of predicted genes are members of families. In some cases, tandemly arrayed genes are 99–100% identical, suggesting an active process of amplification and gene conversion. One end of the chromosome consists of a putative bloodstream-form variant surface glycoprotein (VSG) gene expression site that appears truncated and degenerate. The other chromosome end carries VSG and expression site-associated genes and pseudogenes over 50 kb of subtelomeric sequence where, unusually, the telomere-proximal VSG gene is oriented away from the telomere. Our analysis includes the cataloguing of minor genetic variations between the chromosome I homologues and an estimate of crossing-over frequency during genetic exchange. Genetic polymorphisms are exceptionally rare in sequences located within and around the strand-switches between several gene clusters. |
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