Global analysis of histone variant H2A.Z acetylation in Saccharomyces cerevisiae

The histone variant H2A.Z is an evolutionarily conserved variant which is an essential chromatin component for many organisms. H2A.Z plays a pivotal role in a diverse array of chromatin-based processes such as gene transcription and chromosome segregation. In yeast, H2A.Z is acetylated at four N-terminal lysine residues (K3, K8, K10 and K14). Previous studies have shown that these acetylation sites are critical for H2A.Z function. My research aim was to examine how these four acetylatable lysines act to regulate the function of H2A.Z. Genome mapping of the acetylated K8, K10, K14 isoforms revealed that these acetyl marks are co-localised across the budding yeast genome, indicating that acetylation is a common feature of H2A.Z. Examinations of individual acetylation sites using mutational and phenotypical analyses did not reveal any distinct phenotypes between individual lysine residues. These findings indicated that individual acetylation sites are functionally redundant. Intriguingly, H2A.Z is mis-regulated when all four lysine were mutated to arginine (H2A.Z K3, 8, 10, 14 R) by showing sensitivity to a variety of agents. The global distribution profiles of H2A.Z, however, were unaffected by N-terminal lysine mutations. In fact, unacetylatable H2A.Z alleles perturbed H2A.Z chromatin abundance. Biochemical evidence showed that the altered chromatin level was severely defective when combined unacetylatable allele with mutations of SWR-C components. Together, the data presented here suggested that the N-terminal acetylation of H2A.Z regulates its genome abundance independent of its deposition pathway by SWR-C complex.