Regulation of rRNA Synthesis by TATA-Binding Protein-Associated Factor Mot1

Abstract

Mot1 is an essential, conserved, TATA-binding protein (TBP)-associated factor in Saccharomyces cerevisiae with well-established roles in the global control of RNA polymerase II (Pol II) transcription. Previous results have suggested that Mot1 functions exclusively in Pol II transcription, but here we report a novel role for Mot1 in regulating transcription by RNA polymerase I (Pol I). In vivo, Mot1 is associated with the ribosomal DNA, and loss of Mot1 results in decreased rRNA synthesis. Consistent with a direct role for Mot1 in Pol I transcription, Mot1 also associates with the Pol I promoter in vitro in a reaction that depends on components of the Pol I general transcription machinery. Remarkably, in addition to Mot1's role in initiation, rRNA processing is delayed in mot1 cells. Taken together, these results support a model in which Mot1 affects the rate and efficiency of rRNA synthesis by both direct and indirect mechanisms, with resulting effects on transcription activation and the coupling of rRNA synthesis to processing.

This work was supported by NIH grants GM55763 to D.T.A. and GM63952 to A.L.B. This work was also supported by American Heart Association grant AHA-0555490U to J.S.S.

Special thanks go to Loan Vu for help and advice with the pulse-labeling experiments, to Susan Baserga and Steve Hahn for yeast strains, and to Beth Moorefield for providing yeast strains prior to publication. We are also grateful to members of the Auble and Beyer labs for discussions and comments on the manuscript.