Control of antigenic variation in African trypanosomes.

Antigenic variation of African trypanosomes results from the controlled expression of a single variant cell-surface glycoprotein (VSG) gene from a repertoire of about 1,000 genes. The transcription of the VSG genes occurs uniquely at telomeres, where the expressed VSG gene is part of a large polycistronic transcription unit that appears to be transcribed by a specialized RNA polymerase. Recent developments that enhanced our understanding of the control of VSG gene expression and of the mechanisms of antigenic variation are discussed in this review.