CO-DUPLICATION OF A VARIANT SURFACE GLYCOPROTEIN GENE AND ITS PROMOTER TO AN EXPRESSION SITE IN AFRICAN TRYPANOSOMES

Activation of the metacyclic variant antigen type 7 (MVAT7) variant su rface glycoprotein (VSG) gene in bloodstream Trypanosoma brucei rhodes iense involves a duplicative transposition of the gene. The DNA transp osition unit extends from a site similar to 3.0 kilobases upstream of the VSG gene through the coding region and includes a 73-base pair seq uence that possesses promoter activity in transient transfections. Thi s MVAT7 promoter has 80% identity to a previously characterized promot er for the MVAT4 VSG gene. Nuclear run-on assays demonstrate that the MVAT7 promoter is active in MVAT7 bloodstream organisms and that its t ranscript is synthesized by an RNA polymerase resistant to alpha-amani tin, consistent with previously published reports regarding VSG gene t ranscription. The transcription start site was identified by primer ex tension studies and a modified rapid amplification of cDNA ends protoc ol. Selective mutational analysis of the MVAT7 promoter showed that tw o conserved trinucleotide regions are important for full promoter func tion. This study demonstrates that the MVAT7 VSG gene is co duplicated with its promoter and transcribed into a monocistronic precursor RNA.