Cloning and transcriptional analysis of a variant surface glycoprotein gene expression site in Trypanosoma brucei.

The variant surface glycoprotein (VSG) gene expression site in Trypanosoma brucei variant 117a has been mapped to a point about 40 kb upstream from the VSG gene. Sequences upstream from the previously identified [Cully, D.F. et al. (1985) Cell 42, 173-182] expression site associated gene (ESAG-I) have been cloned and a stable 1.3 kb transcript has been localized immediately 5' to ESAG-I. This transcript is in the same orientation and approximately as abundant as the ESAG-I message. A highly conserved region, of which at least 15 copies are present in the genome, has been identified further upstream. A stable transcript corresponding to this region was not detected in variant 117a, but a 1.7 kb transcript was detected in variant 221a. In isolated nuclei, representative sequences from the 117a, expression site were transcribed unidirectionally at similar rates, and transcription was insensitive to alpha-amanitin.