Chromatin protein methylation in proliferating liver and hepatoma cells

Chromatin protein methylation in proliferating liver cells and hepatomas was examined in vivo and in vitro. Methylation in vivo was estimated using 2-14 C-L-methionine and 3H-methyl-L-methionine. 3H/14C ratios were calculated for crude histone and nonhistone chromatin protein fractions and compared to those calculated for serum albumin. From this, determination of a methylation index was calculated using serum albumin as a standard. Results of this study indicate that both histones and nonhistone chromatin proteins are methylated to a greater extent in proliferating liver cells and in hepatomas than in control preparations. These observations are generally supported by our in vitro methylation studies. The results are discussed in terms of chromatin protein methylation and its possible relationship to DNA replication.