Figure 2.

Histone (H1) kinase activity of fractions incubated separately and in combination. Samples of each fraction were either diluted into extraction buffer or combined with HSS-2 before transfer to 21°C. Aliquots were taken every 10 min for up to 80 min for assay of histone (H1) kinase activity, expressed as picomoles of phosphate transferred per minute per microliter of extract. (A) HSS-2 alone (open squares), HSP-2 alone (green triangles), and HSS-2 recombined with HSP-2 (blue circles). Neither fraction can activate H1 kinase alone but when recombined stimulate one cycle of activation and inactivation of H1 kinase. (B) From a different extract, HSS-2 was recombined with either HSP-2 (blue circles), HSP-1a (brown circles), or HSP-1b (yellow triangles). Only HSP-2 stimulated one cycle of mitotic histone (H1) kinase activation and inactivation when combined with HSS-2.