Methylation, a new epigenetic mark for protein stability.

Recent studies on the lysine methylation of histones have moved rapidly thanks to the discoveries of a variety of histone lysine methyltransferases. Histone lysine methylation is known to either activate or repress gene expression depending upon the position and status of the methylated lysine residue. Recently, an increasing number of lysine methyltransferases have been identified to modify non-histone proteins. Among those enzymes, the most extensively studied is Set9, a SET domain-containing lysine methyltransferase. Set9 was initially found to target histone H3 lysine 4 for monomethylation and was subsequently shown to target a variety of non-histone proteins, especially transcription-related factors. Functional studies revealed that Set9-mediated methylation of different non-histone proteins leads to distinct biological consequences, most of which point to protein stability. Here we summarize the latest findings on the effects of Set9-mediated lysine methylation on the stability of non-histone proteins.