The replicative lifespan-extending deletion of SGF73 results in altered ribosomal gene expression in yeast

Sgf73, a core component of SAGA, is the yeast orthologue of ataxin-7, which undergoes CAG-polyglutamine repeat expansion. leading to the human neurodegenerative disease spinocerebellar ataxia type 7 (SCA7). Deletion of SGF73 dramatically extends replicative lifespan (RLS) in yeast. To further define the basis for Sgf73-mediated RLS extension, we performed ChIP-Seq, identified 388 unique genomic regions occupied by Sgf73, and noted enrichment in promoters of ribosomal protein (RP)-encoding genes. Of 388 Sgf73 binding sites, 33 correspond to 5 regions of genes implicated in RLS extension, including 20 genes encoding RPs. Furthermore, half of Sgf73-occupied, RLS-linked RP genes displayed significantly reduced expression in sgf73 Delta mutants, and double null strains lacking SGF73 and a Sgf73-regulated, RLS linked RP gene exhibited no further increase in replicative lifespan. We also found that sgf73 Delta mutants display altered acetylation of lfhl, an important regulator of RP gene transcription. These findings implicate altered ribosomal protein expression in sgf73 Delta yeast RLS and highlight altered acetylation as a pathway of relevance for SCA7 neurodegeneration.