The Paf1 complex: associated with RNA polymerase II and important for post-transcriptional processes.
Kristi Penheither (1), Cherie Mueller (1), Stephanie Porter (1), Judith Jaehning (2)
(1) Molecular Biology Program, University of Colorado HSC, 4200 E. 9th Ave., Denver, CO, 80262, USA;
(2) Department of Biochemistry and Molecular Genetics, UCHSC
The Paf1 complex is a form of RNAPII that includes Paf1, Cdc73, Ctr9, Rtf1, and Leo1 that is biochemically distinct from the Srb/Med-containing 'holoenzyme'. Loss of Paf1 results in severe phenotypes and reduced abundance of other Paf1 factors. Loss of Paf1 or Rtf1 also results in the subcellular mislocalization of other Paf1 factors, a reduction in Ser2 phosphorylation, and shortened polyA tails. Surprisingly, in rtf1 or cdc73 mutants, which have little phenotype, Paf1 factors are no longer associated with chromatin and are significantly reduced in their association with Pol II. Although Paf1 complex components co-localize with Pol II at the promoters and coding regions of all genes tested, we identified only a small set of genes that appear to be direct targets of Paf1. We examined these primary targets to determine a role for the Paf1 complex in transcription. We found that while the Paf1 complex has been linked to transcriptional initiation and elongation, the promoters of Paf1 target genes are not sensitive to loss of Paf1, and the genes down-regulated in paf1 are not longer or more GC rich than the genome-wide average. These primary Paf1-dependent transcripts do have significantly different half-lives than the bulk population of yeast genes. However, the stability of these transcripts is not affected by loss of Paf1. We are currently investigating the possibility that Paf1's major role is in coordinating transcriptional and post-transcriptional processes.
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