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

We have examined the relationship of phosphate content in histone H1 of Physarum polycephalum to mitotic chromosome condensation and affinity for deoxyribonucleic acid (DNA). H1 undergoes a series of posttranslational phosphorylations which increase its apparent molecular weight on NaDodSO4-polyacrylamide gels. Our studies confirm the observation by Bradbury and co-workers [Bradbury, E. M., Inglis, R. J., Matthews, H. R., & Sarner, N (1973) Eur. J. Biochem. 33, 131-139; Bradbury, E. M., Inglis, R. J., & Matthews, H. R. (1974) Nature (London) 247, 257-261] that the accumulation of phosphate in H1 increases markedly shortly before the onset of mitosis. However, we show in pulse-chase experiments with both 32PO4H1 and [14C]lysine H1 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. We also show that 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.