Reprogramming mRNA expression in response to defect in RNA polymerase III assembly in the yeast Saccharomyces cerevisiae

Interplay between nuclear RNA polymerases is key to growth control. Here, we explored the ways in which mRNA transcription by polymerase II (Pol II) is influenced by a defect in the biogenesis of Pol III. We used the cold-sensitive yeast mutant rpc128-1007, which prevents assembly of the Pol III complex and consequently leads to low tRNA levels. mRNA upregulation in rpc128-1007 cells was generally stronger and involved more genes than downregulation. The observed induction of mRNA expression was mostly indirect and resulted from the de-repression of general control transcription factor Gcn4. mRNA genes that were downregulated by the reduction of Pol III assembly comprise the proteasome complex. We also investigated the ways in which the reprogramming of Pol II genes is influenced by the rpc128-1007 suppressors RBS1 and PRT1, which encode the Pol III assembly factor and the subunit of translation initiation factor eIF3, respectively. Both of the suppressor genes countered the effects of rpc128-1007 on the expression of Gcn4-dependent genes and the effects of PRT1 were stronger than the effects of RBS1. Additionally, Rbs1 modulates Gcn4 activity in a manner that depends on of the Pho85 cyclin Pcl5. We have shown that the downregulation of Pcl5 protein levels by Rbs1 overproduction leads to a Gcn4 response that is likely related to the stabilization of Gcn4 protein. Altogether, our data contribute to the regulatory network which links transcription of different RNA classes Overall design: mRNA analysis in mutant rpc128-1007 and suppressors strains [RBS1], [RBS1-R3H], [PRT1] compared to isogenic wt strain