Topic 8. Control of gene expression

We have identified a heredodimer, Rpb4/7, that functions in transcription, translation and in the two major mRNA decay pathways that operate in the cytoplasm, while shuttling between the nucleus and the cytoplasm. During transcription, Rpb4/7 interacts with the transcripts and later escorts them during their life cycle in the cytoplasm. By modulating binding of various proteins with mRNPs, Rpb4/7 affects the use and fate of these transcripts. At some stage during the mRNA decay pathway, the heterodimer returns to the nucleus to initiate a new round of transcription. We found that the role of Rpb4/7 in the cytoplasm is mechanistically coupled to its role in transcription. Thus, recruitment of Rpb4/7 to Pol II is a prerequisite to its roles in the cytoplasm. Hence, by recruiting Rpb4/7, Pol II governs not only transcription but also translation and mRNA decay. We propose that coupling between mRNA syntheti,c translation and decay machineries is made possible by coordinators whose main role is to control proper levels and usage of mRNAs.