Cell cycle changes in Physarum polycephalum histone H1 phosphate: relationship to deoxyribonucleic acid binding and chromosome condensation

Abstract

The relationship of phosphate content in histone H1 of P. polycephalum to mitotic chromosome condensation and affinity for DNA was examined. H1 undergoes a series of posttranslational phosphorylations which increase its apparent molecular weight on NaDodSO4-polyacrylamide gels. Studies confirm the observation by Bradbury and co-workers that the accumulation of phosphate in H1 increases markedly shortly before the onset of mitosis. However, pulse-chase experiments with both 32PO4 H1 and [14C]lysine H1 showed that there is no significant dephosphorylation of the histone either during or shortly after mitosis, suggesting that nonspecific postmitotic dephosphorylation of H1 is not a prerequisite for chromosome decondensation. Both phosphorylated and unphosphorylated forms of H1 bind with somewhat greater affinity to single-stranded DNA-cellulose than to native DNA-cellulose and that phosphorylation weakens the affinity of H1 to both forms of DNA-cellulose.