ABSTRACT
The four major types of postsynthetic methylation: ϵ-N-methylation of internal lysine residues, guanidino-N-methylation of internal arginine residues, N-methylation of histidine, and O-methylation of carboxyl groups. In an attempt to fractionate radiomethylated nonhistone chromosomal proteins (NHC), C. C. Liew and D. Suria administered methyl-labeled S-adenosylmethionine intraperitoneally to rats in order to obtain exclusive incorporation of labeled N-methyl groups into proteins. For the assessment of in vitro methylation of histones or NHC proteins, most authors have used methyl-labeled S-adenosylmethionine as the precursor. Increased methylation of NHC proteins and histones was observed in transplantable hepatomas, and in rat liver cells in which proliferation was induced by subtotal hepatectomy or by treatment with triiodothyronine. The increased N-acetylation combined with the binding of high mobility group protein alters the structural conformation of the nucleosome so as to make it available for transcription and sensitive to the action of the endonuclease, DNAse I, and micrococcal nuclease.
