Histones H1oa and H1ob are the same as CHO histones H1(III) and H1(IV): new features of H1o phosphorylation during the cell cycle

Abstract

Two histone H1 fractions [H1(I) and H1(II)] and 2 histone H1o fractions (H1oa and H1ob) have been isolated from butyrate-treated Chinese hamster ovary (line CHO) cells by guanidine hydrochloride gradient chromatography on Bio-Rex 70 ion-exchange resin. The fractions was identified by electrophoresis and amino acid analyses. Electrophoretic analysis of cyanogen bromide treated H1o in long acid-urea-polyacrylamide gels suggests that H1oa and H1ob differ, at least, within the 20-30 residue fragment(s) removed by the cyanogen bromide cleavage. Shallow-gradient Bio-Rex 70 chromatography indicates that histones H1oa and H1ob are the same as the respective CHO histones, H1(III) and H1(IV), which were previously resolved. This identification and the phosphate incorporation data revealed new features about H1o phosphorylation. Following release from G1 arrest, H1oa and H1ob become phosphorylated in late G1 prior to DNA synthesis: H1oa and H1ob are phosphorylated at similar rates throughout the cell cycle. Apparently histone H1o is phosphorylated in a cell cycle dependent fashion which mimics that of histone H1.