Eukaryotic DNA is complexed with histone proteins to form nucleosomes. In turn, nucleosomes form chromatin, a highly organised macromolecular structure that allows DNA to exist within the confines of the nucleus. The execution of DNA-based processes, such as replication or transcription, necessitates regulation of its accessibility within chromatin. Therefore, chromatin structure is highly dynamic. A central mechanism of chromatin regulation is through histone post-translational modifications (PTMs). The presence of PTMs is governed by proteins that deposit or remove them (epigenetic writers or erasers), while their downstream functions are carried out by proteins that bind them (epigenetic readers) and mediate a downstream response. Histone PTMs function either individually, or in combination with adjacent marks (histone code hypothesis).

Histone citrullination is a well-established modulator of transcription and chromatin accessibility, however our understanding of the molecular mechanisms through which it operates is in its infancy. Specifically, it is unknown whether epigenetic readers exist that are specific to citrulline marks. Previous studies have demonstrated that the presence of citrullines affects the recruitment of readers to nearby trimethyl-lysines, suggesting that citrulline marks operate within the histone code.

The N-terminal tail of histone H3 is subject to a plethora of PTMs and includes a number of citrullination sites, as well as neighbouring arginine-lysine residues. We will use protein biochemistry and Mass Spectrometry to identify epigenetic readers to histone H3 citrullines and understand the cross-talk between citrullines and adjacent lysine trimethyl and acetyl marks. Our ultimate aim is to understand how citrulline readers and arginine-lysine modification crosstalk function in the context of cancer and stem cell biology.