Activation of the genes for variant surface glycoproteins 117 and 118 in Trypanosoma brucei (original) (raw)
Related papers
The architecture of variant surface glycoprotein gene expression sites in Trypanosoma brucei
Molecular and Biochemical Parasitology, 2002
Trypanosoma brucei evades the immune system by switching between Variant Surface Glycoprotein (VSG) genes. The active VSG gene is transcribed in one of approximately 20 telomeric expression sites (ESs). It has been postulated that ES polymorphism plays a role in host adaptation. To gain more insight into ES architecture, we have determined the complete sequence of Bacterial Artificial Chromosomes (BACs) containing DNA from three ESs and their flanking regions. There was variation in the order and number of ES-associated genes (ESAG s). ESAG s 6 and 7, encoding transferrin receptor subunits, are the only ESAG s with functional copies in every ES that has been sequenced until now. A BAC clone containing the VO2 ES sequences comprised approximately half of a 330 kb 'intermediate' chromosome. The extensive similarity between this intermediate chromosome and the left telomere of T. brucei 927 chromosome I, suggests that this previously uncharacterised intermediate size class of chromosomes could have arisen from breakage of megabase chromosomes. Unexpected conservation of sequences, including pseudogenes, indicates that the multiple ESs could have arisen through a relatively recent amplification of a single ES. #
Control of VSG Gene Expression Sites In Trypanosoma Brucei
Molecular and …, 1998
The basic features of surface coat switching in T. brucei have been amply reviewed in recent years [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] and are summarized in Fig. 2. As most of the genes for Variant Surface Glycoproteins (VSGs) are located in a chromosome-internal position [11], ...
Gene, 1982
The nucleotide sequence of the 5' end of the mRNA for variant surface glycoprotein (VSG) 117 has been determined and compared with the sequence of the unexpressed basic copy (BC) of the VSG 117 gene. This shows the existence of an exon 35 nucleotides long at the 5' end of the mRNA. The evidence suggests that this 'mini-exon' is derived from the expression site into which the VSG 117 BC is transposed during activation. The nucleotide sequence of this mini-exon is indistinguishable from that recently found for a different VSG, 118 (Van der Ploeg et al., Nucl. Acids Res. 10 (1982) 3591-3604). Analysis of the 5' end of the mRNA for another VSG (221) whose gene is thought to be activated by a different mechanism to that of VSGs 117 and 118 indicates that the 5'-most 35 nucleotides of the VSG 221 mRNA are identical to the 117/l 18 mini-exon sequence. The implications of these results for the mechanism of VSG gene expression are discussed.
BMC Genomics, 2007
In a mammalian host, the cell surface of African trypanosomes is protected by a monolayer of a single variant surface glycoprotein (VSG). The VSG is central to antigenic variation; one VSG gene is expressed at any one time and there is a low frequency stochastic switch to expression of a different VSG gene. The genome of Trypanosoma brucei contains a repertoire of > 1000 VSG sequences. The degree of conservation of the genomic VSG repertoire in different strains has not been investigated in detail.
Biochemistry, 1988
Secondary structure determinations have been carried out on two antigenically related variant surface glycoproteins (VSG's) from Trypanosoma brucei, WaTat 1.1 and WaTat 1.12. The two molecules, which bear highly homologous amino-terminal sequences, showed subtle differences in their circular dichroism (CD). Computer analysis revealed that the contribution of a helix to the secondary structure of the VSG's was 49% for WaTat 1.1 and 52% for WaTat 1.12. Unfolding studies using guanidine hydrochloride suggested that the WaTat 1.12 VSG was slightly more resistant than WaTat 1.1 VSG to the effect of this reagent.
International Journal for Parasitology, 2001
African trypanosomes escape the host immune response through a periodical change of their surface coat made of one major type of protein, the variant surface glycoprotein. From a repertoire of a thousand variant surface glycoprotein genes available, only one is expressed at a time, and this takes place in a specialised expression site itself selected from a collection of an estimated 20±30 sites. As the specialised expression sites are long polycistronic transcription units, the variant surface glycoprotein is co-transcribed with several other genes termed expression site-associated genes. How do the trypanosomes only use a single specialised expression site at a time? Why are there two dozen specialised expression sites? What are the functions of the other genes of these transcription units? We review the currently available answers to these questions. q
2007
t Thee genes for the Variant Surface Glycoprotei n (VSG) of Trypanosoma brucei are transcribed in telomericc expression sites (ESs). There are about 20 different ESs per trypanosome nucleus. Usually,, only one is active at a time, but trypanosome s can switch the ES that is active at a low ratee (<10 per cel per generation) . To study activation and silencing of ESs, we have generate d a linee of T. brucei All with three ESs marked with a different drug resistanc e gene. We show that aa selection with any combination of two of these drugs leads to an unstabl e double-resistan t phenotypee in which the two ESs containing the correspondin g marker genes switch backwar d and forwardd at a very high rate (> 10" per cel per generation) . Unstabl e triple-resistant trypanosome s weree not obtained. We conclude that the unstabl e rapid-switching state is a natural intermediat e in ESS switching. It only involves two ESs, whereas the other ESs are not expressed . Furthermor e we ...
Control of variant surface glycoprotein gene-expression sites in Trypanosoma brucei
The EMBO journal, 1999
Trypanosoma brucei has 20 similar telomeric-expression sites for variant surface glycoprotein genes. Expression sites appear to be controlled at the level of transcription initiation, resulting in only one site being active at any time. Switching between expression sites occurs at a low rate. To analyse the switching mechanism, we used trypanosomes with two expression sites tagged with two different drug-resistance genes and selected these on agarose plates containing both drugs. Double-resistant clones arose at a low frequency of 10(-7) per cell, but these behaved as if they rapidly switched between the two tagged expression sites and lost double resistance in the absence of selection. Using in situ hybridization we found that only 10% of the double-resistant cells had two fluorescent spots corresponding to transcribed expression sites. Our results suggest that: (i) a double expressor is not a stable intermediate in expression site switching; (ii) expression sites are not independe...