Histone Monoubiquitylation Position Determines Specificity and Direction of Enzymatic Cross-talk with Histone Methyltransferases Dot1L and PRC2

It is well established that chromatin is a destination for signal transduction, affecting many DNA-templated processes. Histone proteins in particular are extensively post-translationally modified. We are interested in how the complex repertoire of histone modifications is coordinately regulated to generate meaningful combinations of "marks" at physiologically relevant genomic locations. One important mechanism is "cross-talk" between pre-existing histone post-translational modifications and enzymes that subsequently add or remove modifications on chromatin. Here, we use chemically defined "designer" nucleosomes to investigate novel enzymatic cross-talk relationships between the most abundant histone ubiquitylation sites, H2AK119ub and H2BK120ub, and two important histone methyltransferases, Dot1L and PRC2. Although the presence of H2Bub in nucleosomes greatly stimulated Dot1L methylation of H3K79, we found that H2Aub did not influence Dot1L activity. In contrast, we show that H2Aub inhibited PRC2 methylation of H3K27, but H2Bub did not influence PRC2 activity. Taken together, these results highlight how the position of nucleosome monoubiquitylation affects the specificity and direction of cross-talk with enzymatic activities on chromatin. Background: "Designer" nucleosomes are key tools to investigate functions of histone modifications. Results: Histone H2Aub inhibits PRC2 methylation of histone H3 Lys-27 but not Dot1L methylation of H3 Lys-79. Conclusion: The position of nucleosome monoubiquitylation affects the specificity and direction of cross-talk with histone methyltransferases. Significance: Cross-talk between histone modifications and chromatin enzymatic activities may be an important mechanism for generating distinct biological outputs.