Nucleolar and extranucleolar chromatin of rat Novikoff hepatoma cells: A comparison of histone and non-histone protein acetylation

Abstract

Histone acetylation was studied in two nuclear subfractions, nucleoli and the nuclear chromatin, which have substantially different transcriptional activity. The quantitative uptake and turnover of [1- 14C]acetate into the total histone was found not to differ significantly between the two nuclear fractions. Some variations among the relative specific activities of the individual histones were observed after analysis on acrylamide gels, but their significance is questionable due to possible changes in the F 3 dimer/monomer ratio induced by the isolation of histones. All histone fractions were labeled when rat ascites cells were exposed to 3H-labeled amino acids for 1.5 h. In a similar 1.5-h experiment, [1- 14C]acetate was incorporated primarily into the arginine-rich histones F 3 and F2a1; the lysine-rich F1 was unlabeled. Thus, the acetylation observed in these experiments occurred predominantly on pre-formed histone molecules. Nonhistone chromosomal proteins were acetylated to about 25 % of the specific activity of the histones. Only minor differences in the extent of histone acetylation in the isolated nucleoli as compared with nuclear chromatin indicate that histone acetylation is not directly related to the amount of active template in these nuclear subfractions.