Dissecting regulatory mechanisms governing histone H3 lysine 9 methylation

The genomes of eukaryotic organisms are covered by histone proteins, which act as a signalling platform that forms an integral part of the regulation and protection of the genome. The signals are post-translational modifications on histone tails for which there are "writer" and "eraser" enzymes as well as reader proteins that specifically bind the mark. This project focuses on an enzyme family called SUV39, which is at the heart of constitutive heterochromatin systems. We study proteins from human and fission yeast, a very informative model system for understanding the fundamental mechanisms of signalling on chromatin. SUV39 proteins deposit the histone H3 lysine 9 methyl marks (H3K9me), which are required to establish silent epigenetic states that can be propagated from one generation to the next without changes in the underlying DNA sequence. In mammals, SUV39 enzymes have been shown to be required for healthy development and their deregulation is associated with various cancers.

Recent work in our and other laboratories has revealed that specific post-translational modifications, in particular ubiquitination on a residue close to H3K9, lysine 14, can stimulate the activity of the fission yeast SUV39 protein Clr4 on H3K9 by more than 250-fold. We have furthermore evidence, that phosphorylation on Clr4 itself regulates its H3K9 methyltransferase activity. This proposal is a collaborative effort that leverages our expertise in the high-resolution structural approaches of X-ray crystallography and NMR to visualize and understand how these post-translational modifications control SUV39 proteins. We will further determine by NMR the role of various structural states in the regulation of Clr4's activity. This rich understanding of SUV39 proteins will be beneficial to driving efforts forward to develop therapeutic approaches in cancer.

Proteins of the SUV39 family deposit methyl marks on histone H3 lysine 9, which are strongly associated with silent regions of the genome, where it is critical for maintaining transcriptional programs during development and for genome stability through the cell cycle. We have shown that the fission yeast Clr4 and human SUV39 proteins are regulated by the ubiquitination of H3K14, phosphorylation and N-terminal autoinhibition. We will use our expertise in X-ray crystallography and NMR to visualize and reveal the mechanisms through which post-translational modifications like ubiquitination and phosphorylation control the H3K9 methyltransferase activity of SUV39 proteins. We will furthermore develop a molecular biology toolbox to detect and visualize the mono-ubiquitination of H3K14 across cells and genomes. The results of this proposal will boost our fundamental understanding of heterochromatin formation and have the potential to lead to new therapeutic and diagnostic approaches.