An African trypanosome variant surface glycoprotein gene whose expression is not activated by duplication.

A variant surface glycoprotein (VSG) of Trypanosoma brucei is encoded by a gene whose expression is not governed by duplication-transposition. There are two copies of this gene. The 5' flanking regions of the two genes are indistinguishable by restriction mapping, although each possesses approximately 5-10 Kbp of DNA which is devoid of restriction sites. All restriction enzymes tested appeared to cut genomic DNA at a uniform distance 3' of the gene. This, coupled with the observed sensitivity of both genes to BAL 31, indicates that they lie near chromosomal termini. Length variation occurs 3' of these genes in bloodstream clones and their procyclic derivatives, although the number of length variants is conserved. This suggests that length variation alone does not control VSG switching or gene expression and that constraints exist on the extent to which 3' flanking regions can vary in length.