Cell-specific phosphorylation of H1 histone subtypes among different Chinese hamster cell lines in interphase.

The phosphorylation of H1 histone subtypes was studied in 3 Chinese hamster cell lines (CHO, V79, and CHW). Chromatographic resolution of H1 subtypes showed that all 3 cell lines contained 1 homologous (coeluting) H1 subtype (CHO-1, V79-1, and CHW-1) while V79 and CHW cells contained 2 additional H1 subtypes not found in CHO cells (V79-2,3 and CHW-2,3). N-Bromosuccinimide cleavage of 32P-labeled H1 subtypes demonstrated that all V79 subtypes were phosphorylated in both the NH2- and COOH-terminal regions during interphase while CHO-1 was phosphorylated only in the COOH-terminal region. Tryptic phosphopeptide fractionations, using 2 sequential electrophoretic steps on paper, demonstrated qualitative differences in the 32P-labeled peptides from the 7 H1 subtypes of the 3 cell lines. For example, CHO-1 differed from its V79-1 homologue by 1 phosphopeptide and from its CHW-1 homologue by 3 phosphopeptides. Phosphopeptide differences were also observed among the H1 subtypes of both V79 and CHW cells. The results demonstrate that Chinese hamster cell lines phosphorylated H1 histone subtypes differently during interphase and that there is no rigorous functional connection between the phosphorylation of the NH2-terminal region of 1 or all H1 histone subtypes and the initiation of mitosis in Chinese hamster cells.