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Characterization of the esa1 suppressor LYS20 and discovery of its novel nuclear functions


Histone acetyltransferases (HATs) are one class of enzymes that contribute to chromatin structure and function in eukaryotic cells. The MYST family HAT Esa1 is an essential HAT known to be involved in transcriptional silencing, cell cycle progression and DNA repair, along with its role in transcriptional activation. LYS20 was identified as a high copy suppressor of esa1 mutant phenotypes. This marked the discovery of a previously unsuspected role for Lys20, an enzyme that was only known to function in lysine biosynthesis, yet was localized to the nucleus for purposes that remained unclear. Lys20 is a homocitrate synthase (HCS) that catalyzes the first and rate-limiting step in the alpha-amino adipate pathway used by fungi to make lysine. Reported here is a role for Lys20 in DNA damage repair that is mediated through the H2A variant H2A.Z, thereby defining its nuclear roles. Lys20's HCS catalytic activity is not required for its DNA damage functions, but nuclear localization is important for these roles. Collaborative analysis focused around the well- conserved family of HCSs, in particular the S. pombe HCS Lys4. Structural, kinetic and mechanistic insights are provided for Lys4. Further characterization of ESA1 has also been undertaken, bringing to light new genetic interactions focused around H2A its H2A.Z variant. New factors that influence the biochemical activity of Esa1 are also identified. Results reported here contribute to defining connections between metabolism and chromatin functions by demonstrating nuclear roles for a HCS. Further characterization of both the chromatin association factors and the HCS in this interaction is performed to set the stage for the future of similar analyses

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