Novel role for mediator complex subunit Srb5/Med18 in termination of transcription

Abstract

Mediator complex functions at the recruitment as well as the post-recruitment steps of transcription. Here we provide evidence for a novel role of Mediator in termination of transcription. Mediator subunit Srb5/Med18 cross-links to the 5′ and 3′ ends of INO1 and CHA1. In srb5 - cells, recruitment of TATAbinding protein (TBP) and transcription factor IIB (TFIIB) onto the promoter of these genes remained unaffected, but crosslinking of the cleavage-polyadenylation factors Rna15 and Pta1 toward the 3′ end of genes was compromised. In these cells, RNA polymerase II accumulated near the 3′ end of genes and beyond. Transcription run-on analysis confirmed a transcription readthrough phenotype in the absence of Srb5/Med18. These results strongly suggest that Mediator subunit Srb5/ Med18 is required for proper termination of transcription of a subset of genes in budding yeast. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.