Topography of transcription factor complexes on the Saccharomyces cerevisiae 5 S RNA gene

Locations of component proteins of yeast RNA polymerase III transcription factors (TFIII) A, C and B on a 5 S rRNA gene have been determined by site-specific DNA-protein photo-crosslinking. Comparison with a previously analyzed tRNA gene shows that similar nucleoprotein structures assemble on these two genes despite their differently located internal promoter elements. A principal signature of this homology is the placement of the 95 kDA subunit of TFIIIC, which associates with the box A promoter element of the tRNA gene. On the 5 S rRNA gene, the 95 kDa subunit occupies the same space in the absence of a box A sequence, and despite the presence of a box A-like sequence 30 base-pairs further downstream. A 90 kDa component that was not previously recognized as an integral part of TFIIIC has been specifically located at the 3' end of the 5 S rRNA gene.