Proper formation of mRNP requires co-transcriptional loading of proteins onto nascent transcripts. Mutations in several genes involved in mRNA processing, mRNP assembly and nuclear export lead to production of aberrant mRNPs that are retained in transcription site-associated foci. Retention and degradation of transcripts depend on the nuclear exosome of 3’-5’ exonucleases.We have studied connections between mRNP assembly and quality control in the yeast S. cerevisiae using mutants of the THO complex. THO is implicated in co-transcriptional mRNP assembly, but its precise role is not known. Genetic and biochemical data now show that a defective THO complex negatively impacts mRNA 3’-end processing. We are currently trying to understand the relationship between this phenomenon and mRNP quality control. Retention of mRNP in THO mutants is dependent on the nuclear exosome component Rrp6p. Using the solved crystal structure of Rrp6p, we analyze the effect of Rrp6p designer mutations on mRNP retention and decay. So far, we find that Rrp6p mutants deficient in 3’-5 exonucleolytic decay are also deficient in mRNP retention. Finally, evidence is provided that the Trf4p poly(A) polymerase participates in mRNA decay in THO mutants. However, removal of the protein has no effect on mRNP retention. A model for Rrp6p-mediated mRNA surveillance in THO mutants is discussed.
Main Research Area:
Post-transcriptional control of gene expression: mechanisms of mRNA decay, 2006