Fig. 6. Ark1-associated phosphorylation of histone H3 at serine 10 is highest in mitosis. This figure shows a cold kinase assay that uses anti-phospho-serine 10-histone H3 antibodies to detect phosphorylation of serine 10 of histone H3 in immunoprecipitates. Extracts were prepared from cells that were manipulated to be the equivalent of mid-log phase growth state but be enriched in one of four distinct cell cycle stages. IH2117 was blocked at 37°C for 4 hours 15 minutes (G2-phase sample) and released to 25°C for 45 minutes (mitotic sample). In this mitotic sample, 60% of the cells had either condensed chromosomes or were binuclear without septa. IH2116 was blocked at 37°C for 5 hours 30minutes (G1-phase sample). 100 mM hydroxyurea was added to IH2036 and the culture was incubated for 5 hours at 36°C (S-phase sample). The presence of 
-Pk antibodies on the beads or Ark1.PKC protein in the strain used to make the extract is indicated above each lane. The band corresponding to the full length protein is weaker than in Fig. 5B and a number of degradation products appear below Ark1.PkC in the Ark1.PkC panel. Despite this uniform degradation there is dramatic increase in H3SP reactivity in mitotic extracts over the interphase extracts (right-hand panel).
