Hitting the 'mark': interpreting lysine methylation in the context of active transcription.

Histones and their posttranslational modifications (PTMs) play an important role in regulating DNA-templated processes. While some PTMs directly modulate chromatin architecture via charge effects, others rely on the action of reader or effector proteins that can recognize and bind the modification to fulfill distinct cellular outcomes. One PTM that has been well studied with regard to reader proteins is histone lysine methylation - a PTM linked to many DNA-templated processes including transcription, DNA replication and DNA repair. In this review, we summarize the current understanding of how histone lysine methylation is read during the process of active transcription. We also describe how the interpretation of lysine methylation fits into a larger, more complex 'code' of histone PTMs to modulate chromatin structure and function. These insights take into account emerging concepts in the field in an effort to help facilitate future studies.