Genetic Analysis of htzl Synthetic Interaction with set3 and apq12

HTZ1, which encodes the histone H2A variant H2A.Z in Saccharomyces cerevisiae, is dispensable for viability but htz1∆ is synthetic sick or lethal with null alleles of ~200 non-essential genes. The underling mechanisms of most of these genetic interactions are unknown. I dissected the synthetic growth defect between htz1 and histone methyltransferase gene set3 by isolating bypass genetic suppressors of the htz1∆ set3∆ double mutant. A wide array of loss of function suppressors including genes encoding subunits of Hda1 deacetylase complex, SWR1 complex, H2B deubiquitination module of SAGA complex, proteasome subunits, ubiquitin recycler Ubp14, histone methyltransferase Set1 and silencing information regulator Sir3, were isolated. These suppressors were categorized into three phenotypic groups and function through distinct mechanisms. SGA analysis showed that these suppressors displayed relatively extensive suppression across the htz1∆ genetic interaction network but without significant overlap among each other. High copy bypass suppressor screens of htz1∆ set3∆ revealed BDF1, AHC1, CYC8 and RMR1. A genetic suppressor screen of htz1∆ apq12∆ synthetic lethality was conducted to further understand the role of Htz1 during "transcription memory", a model later refuted by other groups after the initial isolation of suppressor. Despite this, the isolated suppressors provide a supplemental understanding to the htz1∆ set3∆ suppressor screen and revealed an interesting group of genetic suppressors which should be valuable for future understanding of the function of Apq12.

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