Research in the Osley laboratory is focused on the role of chromatin in gene expression, DNA replication, and DNA double-strand break repair. We use the model organism, Saccharomyces cerevisiae, to investigate the relationship of histone modifications and nucleosome remodeling to these cellular processes.
Gene expression in growing and quiescent cells: We study the role of histone H2B monoubiquitylation (H2Bub1) and other histone modifications in the regulation of transcription. We have found that H2Bub1 is localized to gene coding regions through the association of the ubiquitylation machinery (Rad6/Bre1) with elongating RNA polymerase II (Pol II). The absence of H2B ubiquitylation leads to a defect in transcription elongation, which we have attributed to a defect in the reassembly of nucleosomes displaced by Pol II. Our recent studies are focused on the role of chromatin structure in the development of quiescent cells that are formed when yeast enters stationary phase following depletion of glucose. These studies are investigating the functional significance of the retention of several histone methylation marks on inactive genes in quiescent cells, with reference to the long-term survival of these cells and their ability to synchronously re-enter the cell cycle.
DNA replication: We study the role of H2B ubiquitylation in DNA replication. We have found that H2Bub1 and the H2B ubiquitin ligase, Bre1, are associated with chromatin adjacent to origins of DNA replication. The absence of H2Bub1 leads to a defect in replication fork progression and replisome instability. We found that H2Bub1 regulates the assembly of nucleosomes on newly replicated DNA, which helps to promote progression of the replication fork.
DNA double-strand break repair: Our studies investigate the role of ATP-dependent nucleosome remodeling in the repair of DNA double-strand breaks (DSBs). We have found that the INO80 nucleosome-remodeling complex promotes the displacement of nucleosomes adjacent to a defined DSB in yeast. This leads to the efficient recruitment of factors that promote homologous recombinational repair (HRR). Our current studies are focused on the role of other nucleosome remodeling factors in earlier events in DSB repair such as the initiation of strand resection that is a prerequisite for HRR.
Trujillo, KT and Osley, MA: A role for H2B ubiquitylation in DNA replication, Mol Cell, 48: 734-746, 2012.
Shieh, GS, Pan, C-H, Wu J-H, Sun, Y-J, Chang, K-W, Tung, L, Chang, T-H, Fleming, A, Hillyer, C, Berger, SL, Osley, MA* and Kao, C-K*: H2B ubiquitylation is part of chromatin architecture that marks exon-intron structure in budding yeast. BMC Genomics. Dec 22;12(1): 627 [epub ahead of print], 2011.
Houghtaling, S, Tsukuda, T, and Osley, MA: Molecular assays to investigate chromatin changes during DNA double-strand break repair in yeast. Methods in Molecular Biology, 745: 79-97, 2011.
Nakanishi, S, Lee, JS, Gardner, JM, Takahashi, Y, Chandrasekharan, Sun, ZW, Osley, MA, Strahl, B, Jasperson, SL, Shilatifard, A: Histone H2BK123 monoubiquitination is the critical determinant for H3K4 and H3K79 trimethylation by COMPASS and Dot1. J Cell Biol, 186: 371-377, 2009.
Tsukuda, T, Lo, Y-C, Krishna, S, Sterk, R, Osley, MA, and Nickoloff, J: INO80-dependent chromatin remodeling regulates early and late stages of mitotic homologous recombination. DNA Repair, 8: 360-360, 2009.
Fleming, AB, Kao, C-F, Hillyer, C, Pikaart, M, and Osley, MA: H2B ubiquitylation plays a role in nucleosome dynamics during transcription elongation. Mol Cell, 31: 57-66, 2008.
Xiao, X, Kao, CK, Krogan, N, Greenblatt, J, Sun, ZW, Osley, MA, and Strahl, B: Rad6-dependent ubiquitylation of H2B is associated with elongating RNA polymerase II. Mol. Cell. Biol. 25: 637-651, 2005.
Tsukuda, T, Fleming, A, Nickoloff, J.A, and Osley, MA: Chromatin remodeling at a DNA double-strand break site in Saccharomyces cerevisiae. Nature 438: 379-383, 2005.