Coupling mRNA Synthesis and Decay

What has been will be again, what has been done will be done again; there is nothing new under the sun. —Ecclesiastes 1:9 (New International Version )IMPORTANCE Posttranscriptional regulation of gene expression has an important role in defining the phenotypic characteristics of an organism. Well-defined steps in mRNA metabolism that occur in the nucleus—capping, splicing, and polyadenylation—are mechanistically linked to the process of transcription. Recent evidence suggests another link between RNA polymerase II (Pol II) and a posttranscriptional process that occurs in the cytoplasm—mRNA decay. This conclusion appears to represent a conundrum. How could mRNA synthesis in the nucleus and mRNA decay in the cytoplasm be mechanistically linked? After a brief overview of mRNA processing, we will review the recent evidence for transcription-coupled mRNA decay and the possible involvement of Snf1, theSaccharomyces cerevisiae ortholog of AMP-activated protein kinase, in this process.