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Investigation into the role and regulation of histone lysine methylation in the yeast Saccharomyces cerevisiae

University of British Columbia

Post-translational modification of histones is one way that chromatin structure is altered to modulate transcription. Histone modifications serve as “marks” on chromatin, which are recognized by specific proteins that have a direct effect on chromatin structure. Lysine methylation is particularly complex and the function and regulation of all lysine methylation marks is not fully understood. Histone H3 lysine 4 tri-methylation (H3K4me3) correlates with patterns of histone acetylation and transcriptional activation. Jhd2 has been identified as the major H3K4me3 histone demethylase (HDM) in S. cerevisiae, but its mechanism during transcriptional repression is unknown. This thesis demonstrates that acetylation of H3 negatively regulates demethylation of H3K4me3 by Jhd2 and provides evidence of crosstalk between lysine acetylation and H3K4me3. Additionally, we provide a potential mechanism for removal of H3K4me3 following gene repression. Several methyl-lysine binding domains have been identified. Isw1 is found as the catalytic subunit of three ATP-dependent chromatin remodelling complexes in S. cerevisiae. These complexes function at different regions of the genome, but the mechanism behind this patterning is uncharacterized. One of these complexes, Isw1b, localizes to the mid- and 3’ regions of genes in a pattern similar to H3K36me3. We demonstrate that the Isw1b subunit, Ioc4, interacts with H3K36me3 through its PWWP domain. This provides a targeting mechanism for Isw1b to specific areas of the genome. NuA3 is a histone acetyltransferase (HAT) complex that has also been demonstrated to interact with H3K36me3. Like, Isw1b, NuA3 contains an auxiliary protein that contains a PWWP domain, Nto2. Our data demonstrates that the Nto2 PWWP domain is the best candidate for NuA3 interaction with H3K36me3, however a direct interaction remains to be shown. We also demonstrate that both H3K4me3 and H3K36me3 are required for interaction of NuA3 with chromatin; thus, the subunits in NuA3 may undergo bivalent interaction with chromatin. These findings provide insight into the regulation of H3K4me3 and the function of H3K36me3 during normal cellular function. H3K4me3 is regulated through crosstalk with lysine acetylation and H3K36me3 targets other chromatin modification complexes to specific areas of the genome.

Text

2011-12-06

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/39481

Genetics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/