A Region of Bdp1 Necessary for Transcription Initiation That Is Located within the RNA Polymerase III Active Site Cleft

Abstract

The RNA polymerase III (pol III)-specific transcription factor Bdp1 is crucial to pol III recruitment and promoter opening in transcription initiation, yet structural information is sparse. To examine its protein binding targets within the pre-initiation complex at the residue-level, photo-reactive amino acids were introduced into yeast Bdp1. Mutations within the highly conserved SANT domain cross-linked to the TFIIB-related transcription factor Brf1, consistent with previous studies. In addition, we identified an essential N-terminal region that cross-linked with the pol III catalytic subunit C128 as well as Brf1. Closer examination revealed this region interacted with the C128 N-terminal region, the N-terminal half of Brf1, and the C-terminal domain of the C37 subunit, together positioning this region within the active site cleft of the pre-initiation complex. With our functional data, our analyses identified an essential region of Bdp1 positioned within the active site cleft of pol III and necessary for transcription initiation.