A link between transcription and mRNP quality in Saccharomyces cerevisiae

The transcription machinery plays a direct role in the assembly of messenger ribonucleoprotein particles (mRNPs), contributing to the loading of proteins onto nascent transcripts. Such mRNP biogenesis is linked to the THO complex that operates at the boundary between transcription and nuclear export. Early mRNP assembly events are subject to surveillance by the nuclear exosome that retains, and degrades, aberrant mRNAs. A yeast strain that carries deletions of Hpr1p and Rrp6p of the THO complex and the nuclear exosome, respectively, grows slowly, possibly due to lack of Rrp6p-dependent mRNA quality control. We selected a number of spontaneous revertant strains from the slow growth phenotype. Interestingly, transcriptional activity was reduced in all revertants. These data corroborate earlier findings that transcriptional down regulation improves growth of cells containing a crippled mRNP formation/surveillance system and illustrates the impact transcriptional activity can have on early mRNP assembly.