Integration of multiple nutrient cues and regulation of lifespan by ribosomal transcription factor Ifh1.

Ribosome biogenesis requires an enormous commitment of energy and resources in growing cells. In budding yeast, the transcriptional coactivator Ifh1p is an essential regulator of ribosomal protein (RP) gene transcription. Here, we report that Ifh1p is dynamically acetylated and phosphorylated as a function of the growth state of cells. Ifh1p is acetylated at numerous sites in its N-terminal region by Gcn5p and deacetylated by NAD(+)-dependent deacetylases of the sirtuin family. Acetylation of Ifh1p is responsive to intracellular acetyl-CoA levels and serves to regulate the stability of Ifh1p. The phosphorylation of Ifh1p is mediated by protein kinase A and is dependent on TORC1 signaling. Thus, multiple nutrient-sensing mechanisms converge on Ifh1p. However, instead of modulating overall rates of RP gene transcription or cell growth, the nutrient-responsive phosphorylation of Ifh1p plays a more prominent role in the regulation of cellular replicative lifespan.