Phosphorylation of H1 facilitates linker histone removal and firing of
replication origins. A, experimental scheme. Macroplasmodia were
treated with okadaic acid as described under “Experimental
Procedures” and then analyzed 1 h after the beginning of S phase.
B, okadaic acid induces hyperphosphorylation of H1. Western blot
analyses of nuclei prepared from macroplasmodia either untreated (–) or
treated (+) with okadaic acid. The blots were probed with an anti-PpH1
antiserum then stripped and reprobed with anti-phospho-H1 antibodies.
C, okadaic acid treatment accelerates global DNA replication. The
effect of okadaic acid treatment on replication was determined by
incorporation of BrdUrd and dot blot analyses of genomic DNA with an
anti-BrdUrd antibody, and blots were quantified with image quant. D,
phosphorylation of H1 regulates replication timing. Replication of Lav2.1 was
monitored by immunoprecipitation (IP) of BrdUrd containing DNA as
described in Fig. 3. Note
lanes 1 and 3 and lanes 2 and 4 correspond
to DNA digested with EcoRI and HindIII, respectively prior to
immunoprecipitation.