The DNA sequence of chromosome I of an African trypanosome: gene content, chromosome organisation, recombination and polymorphism

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.

Histone Acetylation and Methylation at Sites Initiating Divergent Polycistronic Transcription in Trypanosoma cruzi

“…It is conceivable that HH SSRs form specific structures facilitating access to the transcriptional apparatus. The importance of the SSRs is reflected by the rarity of sequence polymorphisms within and around SSRs on chromosome I in T. brucei (41). Also centromere function has been assigned to a SSR on T. cruzi chromosome 3 (42).…”

Human infectivity trait in Trypanosoma brucei: stability, heritability and relationship to sra expression

“…For both crosses, the F1 hybrids fell into one of three phenotypes, fully resistant, fully sensitive or intermediate, demonstrating that this phenotype segregates in the hybrids and is potentially amenable to linkage analysis. A genetic map of TREU 927 is currently being generated with the first two chromosomes, I and II, having been completed (El Sayed et al 2003;Hall et al 2003). Thus it should be possible to identify markers in the genetic map which cosegregate with the phenotype, and so the region of the genome harbouring the gene which determines human serum resistance can be located.…”

Evolutionary Relationships and Protein Domain Architecture in an Expanded Calpain Superfamily in Kinetoplastid Parasites

“…A typical feature of gene organization in trypanosomes and Leishmania is the presence of gene clusters containing several copies of identical or paralogous genes as tandem repeats (Myler et al 1999;El-Sayed et al 2003;Hall et al 2003;Worthey et al 2003). Often, syntenic groups are conserved between different trypanosomatid species (Bringaud et al 1998).…”

“…Repetitive gene families in kinetoplastids are not unusual and are a characteristic feature of their genome organization (Myler et al 1999;El-Sayed et al 2003;Hall et al 2003;Worthey et al 2003). However, in most cases identical or near-identical copies with presumably redundant functionality form the basis of the presence of multicopy gene clusters.…”