Transcripts from the co-transposed segment of variant surface glycoprotein genes are in Trypanosoma brucei polyribosomes.

In Trypanosoma brucei the 5' proximal flanking sequences of a variant surface glycoprotein (VSG) gene, the co-transposed segment, are transcribed in a variant antigenic type- and stage-specific fashion along with the VSG gene. The precursor transcripts are subsequently processed to yield smaller transcripts from the co-transposed segment as well as the VSG mRNA. These co-transposed segment transcripts are quite abundant, polyadenylated and contain the spliced leader sequence, all characteristics of trypanosome mRNAs. We have found that all of the co-transposed segment transcripts from two VSG genes are present in polyribosomes. The nucleotide sequence of much of the co-transposed segment of one of these VSG genes, however, has no open reading frames coding for proteins longer than 49 amino acids. These results suggest that co-transposed segment transcripts do not encode essential proteins even though they are present in polyribosomes and may be translated.