Relationship between H1 histone phosphorylation and genome replication in a mouse-Chinese hamster somatic cell hybrid

The relationship between stable genome replication and the presence of species-specific H1 and H2b histones was studied in a mouse-Chinese hamster somatic cell hybrid (LMC-1). LMC-1 contained the complete chromosome complements of the mouse (LM/TK-, 46 chromosomes) and Chinese hamster (CHW-1102, 22 chromosomes) parents. No chromosome loss occurred in over a year in continuous culture, and both mouse and Chinese hamster enzymes were expressed. Chromatographic resolution of H1 histone subtypes showed that only mouse H1 genes were expressed. Resolution of chromatographically purified H2b histone variants using Triton X-100-containing gels also demonstrated that LMC-1 cells made mouse, not Chinese hamster, H2b histones. Species-specific tryptic phosphopeptides were resolved from purified H1 histones using high voltage paper electrophoresis. These studies demonstrated that characteristic mouse, but not Chinese hamster, phosphopeptides were formed in H1 histones in actively-growing LMC-1 cells. We conclude that the Chinese hamster genome may replicate in a stable manner in the presence of mouse H1 (and H2b) histones, and that there is no obligatory relationship between species-specific phosphorylation of H1 histones and stable genome replication.