Rim15-dependent activation of Hsf1 and Msn2/4 transcription factors by direct phosphorylation in Saccharomyces cerevisiae

•Rim15 activates Hsf1 target genes upon glucose starvation.•Rim15 phosphorylates Hsf1 in vitro.•Igo1 and Igo2 stabilize the transcripts of Hsf1 target genes upon glucose starvation.•Rim15 phosphorylates Msn2, but not Gis1, in vitro.•Rim15 and Yak1 phosphorylate different sites of Hsf1 and Msn2. Rim15 kinase, a downstream effector of PKA and TORC1 signaling pathways, initiates the quiescent program upon nutrient starvation via induction of genes whose expression depends on transcription factors Msn2, Msn4, and Gis1. Here, we demonstrate that Rim15 also induces expression of Hsf1 target genes upon glucose depletion by both transcriptional activation and stabilization of the transcripts. Rim15 phosphorylates Hsf1 in vitro, suggesting that Rim15 might directly activate Hsf1. In addition, Igo1 and Igo2, Rim15 substrate proteins involved in mRNA stabilization, regulate mRNA levels of Hsf1 target genes. We also show that Rim15 can phosphorylate Msn2, but not Gis1, in vitro, implying different mechanisms for the activation of these transcription factors. Rim15phosphorylatesMsn2 by protein kinase assay (View interaction) Rim15phosphorylatesIgo1 by protein kinase assay (View interaction) Rim15phosphorylatesHsf1 by protein kinase assay (View interaction) Yak1phosphorylatesHsf1 by protein kinase assay (View interaction)