CELL CYCLE-DEPENDENT SUPPRESSIVE EFFECT OF HISTONE H1 ON MITOSIS-SPECIFIC H3 PHOSPHORYLATION

To analyze the mechanism by which histone H3 phosphorylation occurs sp ecifically during mitosis, the effect of H1 on mitosis-specific H3 pho sphorylation (Ser-10) was investigated in nucleosomes. Hl interaction with H1-depleted nucleosomes suppressed H3 phosphorylation including S er-10 by approximately 50%. However, H1 interaction with DNA-free hist one octamers failed to suppress H3 phosphorylation. The extent of supp ression of H3 phosphorylation in nucleosomes with H1 prepared from syn chronized HeLa cells was cell cycle-dependent. Binding with a highly p hosphorylated mitotic H1 produced the least suppression of H3 phosphor ylation, whereas binding with a lower H1 phosphorylation from G1 phase resulted in the greatest suppression. The results suggest that 1) mit otic H3 phosphorylation is suppressed with a lower level of H1 phospho rylation during interphase and 2) highly phosphorylated H1 during mito sis partially releases the suppression of mitotic H3 phosphorylation.