The Saccharomyces cerevisiae phosphatase activator RRD1 is required to modulate gene expression in response to rapamycin exposure.

We show that mutants lacking either the phosphatase activator Rrd1 or the phosphatase Pph3 are resistant to rapamycin and that double mutants exhibit a synergistic response. This phenotype could be related to an inability of the mutants to degrade RNA polymerase II, leading to transcription of critical genes that sustain growth.