Arginine/lysine-methyl/methyl switches: biochemical role of histone arginine methylation in transcriptional regulation.

Post-translational modifications (PTMs) are commonly used to modify protein function. Modifications such as phosphorylation, acetylation and methylation can influence the conformation of the modified protein and its interaction with other proteins or DNA. In the case of histones, PTMs on specific residues can influence chromatin structure and function by modifying the biochemical properties of key amino acids. Histone methylation events, especially on arginine- and lysine-residues, are among the best-characterized PTMs, and many of these modifications have been linked to downstream effects. The addition of a methyl group to either residue results in a slight increase in hydrophobicity, in the loss of a potential hydrogen-bond donor site and, in the alteration of the protein interaction surface. Thus far, a number of protein domains have been demonstrated to directly bind to methylated lysine residues. However, the biochemical mechanisms linking histone arginine methylation to downstream biological outputs remain poorly characterized. This review will focus on the role of histone arginine methylation in transcriptional regulation and on the crosstalk between arginine methylation and other PTMs. We will discuss the mechanisms by which differentially methylated arginines on histones modulate transcriptional outcomes and contribute to the complexity of the 'histone code'.