Role of Uhrf1 and histone H3 ubiquitylation in replicative DNA methylation

Genome and epigenome need to be faithfully duplicated to maintain genetic information and cell identity through generations. Unrepaired errors in DNA and chromatin replication lead to genomic instability that causes several diseases as cancer. Epigenetic marks comprise methylation of cytosine within DNA and many types of post-translational modifications (PTMs) of histones tails within nucleosomes, that control chromatin accessibility and regulate gene activity. Examining proteins ubiquitylated on chromatin during DNA replication reaction, Gambus lab identified histone H3 ubiquitylation on lysine 18 and 23 (K18 and K23) as the most abundant ubiquitylated protein during DNA replication in Xenopus egg extract. This modification has been reported by others to be a result of action of Uhrf1 ubiquitin ligase and be required for DNA methylase DNMT1 to fully methylate hemi-methylated DNA after replication. Although the role of Uhrf1 and Dnmt1 in inheritance of DNA methylation patterns is clear, the exact mechanism remains to be dissected. The aim of my project is understanding the mechanism by which Uhrf1 and histone H3 ubiquitylation leads to maintenance of DNA methylation during DNA replication. To investigate this mechanism, I am going to use Xenopus laevis egg extract model system, which allows for biochemical manipulation of DNA replication reaction in very synchronous setting.