SAGA histone acetyltransferase module facilitates chromatin accessibility to SMC5/6

Abstract

Structural Maintenance of Chromosome (SMC) complexes are molecular machines driving chromatin organization at higher levels. In eukaryotes, three SMC complexes (cohesin, condensin, and SMC5/6) play key roles in cohesion, condensation, replication, transcription and DNA repair. Here, we performed a fission yeast genetic screen to identify novel factors required for the SMC5/6 complex with compromised binding to DNA. We identified 79 genes of which the histone acetyltransferases (HATs) were the most represented. Genetic and phenotypic analyses suggested a particularly strong functional relationship between SMC5/6 and SAGA complexes. Furthermore, several SMC5/6 subunits physically interacted with SAGA HAT module components Gcn5 and Ada2. As Gcn5-dependent acetylation facilitates accessibility of chromatin to DNA repair proteins, we first analyzed the formation of DNA damage-induced SMC5/6 foci in the Δgcn5 mutant. The SMC5/6 foci formed normally in Δgcn5, suggesting SAGA-independent SMC5/6 localization to DNA damaged sites. In unchallenged cells, we used Nse4-FLAG chromatin-immunoprecipitation (ChIP-seq) analysis to assess SMC5/6 distribution. A significant portion of SMC5/6 accumulated within gene regions in WT cells, and it was reduced in Δgcn5 and Δada2 mutants. The drop in SMC5/6 levels was also observed in gcn5-E191Q acetyltransferase-dead mutant, suggesting that the SAGA HAT module may facilitate chromatin accessibility to SMC5/6.