Roles of the yeast Ccr4‐Not complex in regulating transcription

Abstract

The highly conserved Ccr4‐Not complex has been ascribed many functions, from transcription regulation to mRNA decay. Initial studies described a role of this complex in preinitiation complex formation, but a number of studies have clearly shown Ccr4‐Not mediates deadenylation of mRNAs and protein ubiquitylation in the cytoplasm. It is still not clear how Ccr4‐Not regulates gene expression, and which of these functions are controlled directly by this complex. Our study demonstrates that Ccr4‐Not complex directly regulates PolII‐dependent transcription elongation. Using purified Ccr4‐Not complex and yeast PolII in an in vitro transcription system we have studied how this complex affects transcription elongation. Our studies show the complex binds directly to the elongation complex, which is partially dependent on the emerging transcript, and crosslinking studies show it also makes contacts with the transcript. Using transcription run on assays, we demonstrate that Ccr4‐Not affects the rate of PolII transcription and stimulates elongation through transcription blocks. Our in vitro results are substantiated by in vivo studies, showing that Ccr4‐Not co‐purifies with PolII and associates with the open reading frames of transcribing genes. Together these studies support a model by which the Ccr4‐Not complex directly associates with transcribing PolII and regulates elongation. Funded by NIH (GM58672).