TORC1 and TORC2 converge to regulate the SAGA co‐activator in response to nutrient availability

Gene expression regulation is essential for cells to adapt to changes in their environment. Co‐activator complexes have well‐established roles in transcriptional regulation, but less is known about how they sense and respond to signaling cues. We have previously shown that, in fission yeast, one such co‐activator, the SAGA complex, controls gene expression and the switch from proliferation to differentiation in response to nutrient availability. Here, using a combination of genetic, biochemical, and proteomic approaches, we show that SAGA responds to nutrients through the differential phosphorylation of its Taf12 component, downstream of both the TORC1 and TORC2 pathways. Taf12 phosphorylation increases early upon starvation and is controlled by the opposing activities of the PP2A phosphatase, which is activated by TORC1, and the TORC2‐activated Gad8 AKT kinase. Mutational analyses suggest that Taf12 phosphorylation prevents cells from committing to differentiation until starvation reaches a critical level. Overall, our work reveals that SAGA is a direct target of nutrient‐sensing pathways and has uncovered a mechanism by which TORC1 and TORC2 converge to control gene expression and cell fate decisions. Synopsis The Schizosaccharomyces pombe SAGA co‐activator regulates gene expression and cell fate decisions in response to nutrient availability. This study shows that TORC1 and TORC2 modulate the phosphorylation of the SAGA subunit Taf12, to control commitment to sexual differentiation upon starvation. SAGA regulates nutrient‐responsive genes downstream of TORC1 and TORC2. Starvation induces phosphorylation of a core SAGA component, Taf12, to control the timing and the amplitude of the differentiation response. Taf12 phosphorylation is tuned by the opposing activities of the TORC1‐PP2A and TORC2‐AKT signaling pathways. Graphical Abstract The Schizosaccharomyces pombe SAGA co‐activator regulates gene expression and cell fate decisions in response to nutrient availability. This study shows that TORC1 and TORC2 modulate the phosphorylation of the SAGA subunit Taf12, to control commitment to sexual differentiation upon starvation.