A ribosomal DNA promoter replacing the promoter of a telomeric VSG gene expression site can be efficiently switched on and off in T. brucei

Ribosomal DNA (rDNA) located in place of the promoter of a variant surface glycoprotein (VSG) expression site of Trypanosoma brucei (T. brucei) has the same functions as the VSG promoters. The T. brucei variants containing rDNA are infective and similar to the wild-type parasites in human blood. However, the structure of the rDNA and the VSG promoter are different. The switching between different VSG expression sites is probably due to telomeric silencing. The suppression of the VSG expression sites occurs during transcription initiation.