Phenotypic analysis of Paf1/RNA polymerase II complex mutations reveals connections to cell cycle regulation, protein synthesis, and lipid and nucleic acid metabolism

Abstract.

Paf1 is an RNA polymerase II-associated protein in yeast, which defines a complex that is distinct from the Srb/Mediator holoenzyme. The Paf1 complex, which also contains Ctr9, Cdc73, Hpr1, Ccr4, Rtf1 and Leo1, is required for full expression of a subset of yeast genes, particularly those responsive to signals from the Pkc1/MAP kinase cascade. We have extensively characterized the pleiotropic phenotypes of deletion mutants for factors present in the Paf1 complex, identifying more than a dozen new phenotypes, and, in some cases, establishing possible molecular explanations for the growth defects. For example, paf1 Δ causes sensitivity to hydroxyurea; this phenotype correlates with a reduction in RNR1 transcript abundance and is suppressed by over-expression of RNR1. In contrast, the resistance of paf1 Δ cells to the transcription elongation inhibitors 6-azauracil and mycophenolic acid correlates with its ability to derepress the IMD2 transcript. We tested the hypothesis that Paf1 communicates with some promoters through the DNA-binding factors Swi4, Mbp1 or Rlm1. The phenotypes of mutations in Paf1 complex components are exacerbated in the swi4 Δ background, suggesting that the complex acts in a pathway parallel to that controlled by Swi4. Conversely, the fact that mbp1 Δ and rlm1 Δ mutations do not enhance the phenotypes suggests that the Paf1 complex may function in the same regulatory pathway(s) with Mbp1 and Rlm1.