Résumé
In the last few years, the discovery of lysine and arginine methylation in histones and other proteins and the enzymes that carry out these posttranslational modifications has added a new dimension to the signal transduction field. In particular, there has been a huge surge in our understanding of how methylation of nucleosomal histones at specific lysine or arginine residues affects chromatin conformations and either facilitates or inhibits transcription from neighboring genes. It appears that the responsible methyltransferases can be targeted in some cases to specific genes and in other cases to broader regions of euchromatin or heterochromatin. Methylation of histones is mechanistically linked to other types of histone modifications, such as acetylation, phosphorylation, and monoubiquitylation; combinations of these modifications cooperate to regulate chromatin structure and transcription by stimulating or inhibiting binding of specific proteins. Although lysine methylation has thus far been observed almost exclusively on histones, arginine methylation has been observed on a variety of other proteins associated with gene regulation, including DNA-binding transcriptional activators, transcriptional coactivators, and many RNA binding proteins involved in RNA processing, transport, and stability. Thus, lysine and arginine methylation of proteins, like many other types of posttranslational modifications, are regulated steps of many specific signaling pathways.