The NuA4 histone acetyltransferase complex is required for gene regulation, cell cycle progression, and DNA repair. Dissection of the 13-subunit complex reveals that the Eaf7 subunit bridges Eaf5 with Eaf3, a H3K36me3-binding chromodomain protein, and this Eaf5/7/3 trimer is anchored to NuA4 through Eaf5. This trimeric subcomplex represents a functional module, and a large portion exists in a native form outside the NuA4 complex. Gene-specific and genome-wide location analyses indicate that Eaf5/7/3 correlates with transcription activity and is enriched over the coding region. In agreement with a role in transcription elongation, the Eaf5/7/3 trimer interacts with phosphorylated RNA polymerase II and helps its progression. Loss of Eaf5/7/3 partially suppresses intragenic cryptic transcription arising in set2 mutants, supporting a role in nucleosome destabilization. On the other hand, loss of the trimer leads to an increase of replicationindependent histone exchange over the coding region of transcribed genes. Taken together, these results lead to a model where Eaf5/7/3 associates with elongating polymerase to promote the disruption of nucleosomes in its path, but also their refolding in its wake.

H2A.Z does not appear to have a role in GAL1 transcriptional memory, but it does have both acetylation-dependent and acetylation-independent roles in GAL1 induction and expression.

Chromatin can be modified by posttranslational modifications of histones, ATP-dependent remodeling, and incorporation of histone variants. The Saccharomyces cerevisiae protein Yaf9 is a subunit of both the essential histone acetyltransferase complex NuA4 and the ATP-dependent chromatin remodeling complex SWR1-C, which deposits histone variant H2A.Z into euchromatin. Yaf9 contains a YEATS domain, found in proteins associated with multiple chromatin-modifying enzymes and transcription complexes across eukaryotes. Here, we established the conservation of YEATS domain function from yeast to human, and determined the structure of this region from Yaf9 by x-ray crystallography to 2.3 Å resolution. The Yaf9 YEATS domain consisted of a ␤-sandwich characteristic of the Ig fold and contained three distinct conserved structural features. The structure of the Yaf9 YEATS domain was highly similar to that of the histone chaperone Asf1, a similarity that extended to an ability of Yaf9 to bind histones H3 and H4 in vitro. Using structure-function analysis, we found that the YEATS domain was required for Yaf9 function, histone variant H2A.Z chromatin deposition at specific promoters, and H2A.Z acetylation.

The incorporation of histone variants into nucleosomes represents one way of altering the chromatin structure to accommodate diverse functions. Histone variant H2A.Z has specific roles in gene regulation, heterochromatin boundary formation, and genomic integrity. The precise features required for H2A.Z to function and specify an identity different from canonical H2A remain to be fully explored. Analysis of the C-terminal docking domain of H2A.Z in Saccharomyces cerevisiae using epistatic miniarray profile (E-MAP) uncovered nuanced requirements of the H2A.Z C-terminal region for cell growth when additional genes were compromised. Moreover, the H2A.Z(1-114) truncation, lacking the last 20 amino acids of the protein, did not support regular H2A.Z functions, such as resistance to genotoxic stress, restriction of heterochromatin in its native context, GAL1 gene activation, and chromatin anchoring. The corresponding region of H2A could fully rescue the strong defects caused by loss of this functionally essential region in the C terminus of H2A.Z. Despite the dramatic reduction in function, the H2A.Z(1-114) truncation still bound the H2A.Z deposition complex SWR1-C, the histone chaperone Chz1, and histone H2B. These data are consistent with a model in which retaining the variant in chromatin after its deposition by SWR1-C is a crucial determinant of its function.