SPECIFIC BINDING OF PROTEINS TO THE NONCODING STRAND OF A CRUCIAL ELEMENT OF THE VARIANT SURFACE GLYCOPROTEIN, PROCYCLIN, AND RIBOSOMAL PROMOTERS OF TRYPANOSOMA-BRUCEI

The variant surface glycoprotein (VSG) and procyclin promoters of Tryp anosoma brucei recruit an RNA polymerase sharing characteristics with polymerase I, but there is no sequence homology between them nor betwe en these promoters and ribosomal promoters. We report the detailed cha racterization of the VSG promoter. The 70-bp region upstream of the tr anscription start site was sufficient for full promoter activity. Muta tional analysis revealed three short critical stretches at positions - 61 to -59 (box 1), -38 to -35 (box 2), and -1 to +1 (start site), the spacing of which was essential. These elements were conserved in the p romoter for a metacyclic VSG gene. Hybrid sequences containing box 1 o f the VSG promoter and box 2 of the ribosomal promoter were active. A specific binding of proteins to the noncoding strand of box 2, but not to double-stranded DNA, occurred. Competition experiments indicated t hat these proteins also bind to the corresponding region of the metacy clic VSG, procyclin, and ribosomal promoters. Binding of such a protei n, of 40 MDa, appeared to be shared by these promoters.