Installation of site-specific methylation into histones using methyl lysine analogs.

Chromatin structure is influenced by post-translational modifications on histones, the principal basic protein component of chromatin. In order to study one of these modifications, lysine methylation, in the context of reconstituted chromatin, this unit describes the installation of analogs of methyl lysine residues into recombinant histones. The modification site is specified by mutating the lysine of interest to cysteine. The mutant histones are expressed and purified, and the cysteine residue alkylated to produce N-methyl aminoethylcysteine, an isosteric analog of methyl lysine. Using different alkylating reagents, it is possible to install analogs of mono-, di-, or trimethyl lysine. While these analogs are not identical to methyl lysine residues, they show similar biochemical properties to their natural counterparts. The ease of synthesis of methyl lysine analog (MLA) histones, especially on a large scale, makes them particularly useful reagents for studying the effects of histone lysine methylation on chromatin structure, biophysics and biochemistry.