Regulators of Cellular Levels of Histone Acetylation in Saccharomyces cerevisiae

Abstract

Histone acetylation levels are regulated through the opposing activities of histone acetyltransferases (HATs) and deacetylases (HDACs). While much is known about gene-specific control of histone acetylation, little is understood about how total or cellular levels of histone acetylation are regulated. To identify regulators of cellular levels of histone acetylation, we developed an immunofluorescence-based approach to screen the single-gene deletion library of Saccharomyces cerevisiae for strains with significant reductions in cellular histone acetylation levels. Of the 4848 mutants screened, we identified 63 strains with considerable cellular hypoacetylation of N-terminal lysines in histones H3 and H4. The cellular hypoacetylation was validated for subsets of the identified strains through secondary screens including mass spectrometric analysis of individual lysines and chromatin immunoprecipitation of specific genomic loci. Among the identified mutants were several members of the Ccr4-Not complex, V-type ATPases, and vacuolar protein-sorting complexes as well as genes with unknown functions. We show that Gcn5, a major HAT in yeast, has diminished histone acetyltransferase activity in particular mutants, providing a plausible explanation for reduction of cellular acetylation levels in vivo. Our findings have revealed unexpected and novel links between histone acetylation, Gcn5 HAT activity, and diverse processes such as transcription, cellular ion homeostasis, and protein transport.

The glucanosyltransferase Gas1 functions in transcriptional silencing

“…Decreased levels of tetraacetylated H3 and H4 were reported for gas1⌬ mutants when assayed by mass spectrometry (37). However, in directed studies with isoformspecific histone antibodies for multiple acetylated lysines, including H4K16, which is required for telomeric silencing, we detected no differences in acetylation in gas1⌬ mutants (Fig.…”

“…A recent study provides another link between Gas1 and chromatin modification, as gas1⌬ and a number of other mutants are implicated in regulation of total acetylation levels of histone H3 and H4 (37). Decreased levels of tetraacetylated H3 and H4 were reported for gas1⌬ mutants when assayed by mass spectrometry (37).…”

The Ccr4–Not complex

“…These complexes contain several Taf subunits in common with TFIID, but also many other subunits (such as the Spt or Ada subunits) including the Gcn5 histone acetyltransferase (HAT) and a deubiquitinating enzyme (Ubp8 in yeast). Examples of these connections are the observation that the N-terminal region of Not2 associates with components of the Gcn5 HAT, whilst Ccr4, Not4 and Not5 were identified as important for global histone acetylation states (Peng et al, 2008). In addition, one of the Spt subunits, namely Spt3, mediates transcriptional phenotypes associated with a mutation in Not1 (Collart, 1996;James et al, 2007).…”

Chromatin: a capacitor of acetate for integrated regulation of gene expression and cell physiology

“…Interestingly, a screen of yeast gene knockout collection for mutants with low global histone acetylation levels identified several members of the Vacuolar-type H + -ATPase (V-ATPase) [33]. This proton pump uses the energy of ATP hydrolysis to transport protons across intracellular and plasma membranes into the vacuole or to the extracellular space.…”