Histone modifications are important determinants of tumorigenesis through their association with gene expression, replication, DNA repair and cell cycle control. We are interested in how chromatin structure contributes to epigenetic regulation of biological functions, including gene transcription, DNA synthesis, cell cycle control and cell differentiation.

Our previous studies have shown that ubiquitylation of H2B (H2Bub) plays roles in both transcription initiation and elongation in Saccharomyces cerevisiae, an activity partly mediated through its regulation of H3 lysine 4 methylation. H2B ubiquitylation is mediated by E2 ubiqutin-conjugating enzyme, Rad6 and E3 ubiquitin ligase, Bre1. Rad6 function is necessary for meiosis through its control of H2B ubiquitylation. The effect of this H2B C-tail modification is at recruiting and stabilizing DNA double strain break (DSB) machinery during meiosis. DSB also happens subject to external agents such as ionizing radiations or chemical insult or other internal mechanism such as conversion of single-strain breaks during replication. H2B ubiquitin conjugating site is at lysine 123 which is surrounded by several amino residues that are subject to phosphorylations, including T122, Y124, S125, S126, S127, and T128. There are cross-regulations between histone modifications. One such regulationis that phosphorylation of histone H3 Ser 10 has been shown to inhibit lys 9 methylation and promote lys 14 acetylation at the same . It is named “cis-regulations of histone modifications”. ?We have identified that H2Bub1 is implicated in regulating cell cycle progression and T122 and T128 are shown the interactions with H2Bub. We hypothesize that H2Bub may be regulated by the phosphorylation of those surrounding residues. We propose to investigate (i) the modification identities of T122, Y124, S125, S126, S 127, and T128 located at histone H2B C-tail; (ii) the interaction between H2Bub1and the potential phosphorylations at H2B C-tail and (iii) the biological functions and the regulatory mechanisms of these interactions.

Transcription of the Ribosomal protein genes (RPG) is coordinately regulated in accord with the cellular growth rate in a manner that requires protein kinase A and the TOR pathway. In addition, RPG transcription is rapidly and coordinately regulated in response to a variety of environmental alterations such as carbon source upshift, heat shock, amino-acid starvation and osmotic shock. In spite of the biological importance of coordinated regulation of RPGs, the mechanism of this regulation is rather incomplete. Our ongoing work has linked the monoubiquitylation of histone H2B K123 (H2Bub) to specific regulations of RP gene expression. H2Bub has been associated with transcription elongation with its role in the regulation of nucleosome dynamics. We performed two genome-wide approaches. First, we used transcription microarrays to identify gene targets that might be regulated by H2Bub. A specific subset of RP genes were overrepresented in genes associated with structural molecule activity. Second, using genome wide ChIP-chip assay, we identified that the levels of H2Bub were enriched throughout the transcribed regions. H2B ubiquitylation also preferentially correlated with of highly transcribed genes, including RPG. To address the physiological significance of the disturbed expression of RPG in the absence of H2Bub, we also domonstrated that ubiquitylated H2B was required for effective polyribosome assembly during protein translation. Taken together, we indentified a central role for H2B ubiquitylation in regulating the specialization of RPG transcription and contribute to ribosomal synthesis. We, therefore, hypothesize that H2Bub may contribute to microregulation of RPG transcription. To test our hypotheses, we propose two specific aims focused on elucidating the role of H2Bub in RPG expression:
Specific Aim 1: To test the hypothesis that H2Bub may contribute to establish the microenvironment of RP gene loci which lead to specific program of RPG expression.
Specific Aim 2: To test the hypothesis that H2Bub may couple transcription apparatus and mRNA processing in regulating RPG expression.