The Ras/PKA signaling pathway directly targets the Srb9 protein, a component of the general RNA polymerase II transcription apparatus.

RNA polymerase II transcription is a complex process that is controlled at multiple levels. The data presented here add to this repertoire by showing that signal transduction pathways can directly regulate gene expression by targeting components of the general RNA polymerase II apparatus. In particular, this study shows that the Ras/PKA signaling pathway in Saccharomyces cerevisiae regulates the activity of the Srb complex, a regulatory group of proteins that is part of the RNA polymerase II holoenzyme. Genetic and biochemical data indicate that Srb9p is a substrate for PKA and that this phosphorylation modulates the activity of the Srb complex. The Srb complex, like many components of the RNA II polymerase machinery, is responsible for regulating the expression of a relatively large number of genes. Thus, this type of a transcriptional control mechanism would provide the cell with an efficient way of bringing about broad changes in gene expression.