Intricate regulation of ribosome biogenesis genes in response to mTORC1 signaling

Genes encoding ribosomal proteins are repressed in response to inhibition of mTORC1. In Saccharomyces cerevisiae , this involves dissociation of the activator Ifh1p in a process that depends on Utp22p, a protein that also functions in pre-rRNA processing. Ifh1p has a paralog, Crf1p, which can mediate mTORC1 inhibition by acting as a repressor. Ifh1p and Crf1p derive from a common ancestor, which may have acted as both an activator and a repressor. We report here that UTP22 and RRP7 , which encodes another pre-rRNA processing factor, are controlled by mTORC1; both gene promoters are bound by Ifh1p, which dissociates on mTORC1 inhibition. Notably, Crf1p acts as an activator as evidenced by reduced expression in a crf1Δ strain. By contrast, Crf1p is required to repress expression of HMO1 , which encodes a cofactor involved in communicating mTORC1 activity to target genes. Our data therefore indicate that Crf1p exhibits the dual repressor/activator functions of the Ifh1p-Crf1p ancestor. ### Competing Interest Statement The authors have declared no competing interest.