Introduction to the multi-author review on methylation in cellular physiology.

Protein post-translational modifications (PTMs) have long been a topic of intensive investigation. Covalent additions to the 20 genetically encoded amino acids can alter protein interactions and can even change enzymatic function. In eukarya, PTMs can amplify both the complexity and functional paradigms of the cellular environment. Therefore, PTMs have been of substantial research interest, both for understanding fundamental mechanisms and to provide insight into drug design. Indeed, targeting proteins involved in writing, reading, and erasing PTMs important for human pathologies are some of the most fruitful avenues of drug discovery. In this multi-author review, we explore exciting new work on lysine and arginine methylation, molecular and structural understanding of some of the lysine and arginine methyltransferases (KMTs and PRMTs, respectively), novel insights into nucleic acid methylation, and how the enzymes responsible for writing these PTMs and readers responsible for recognizing these PTMs could be drugged. Here, we introduce the background and the topics covered in this issue.