Figure 4.

cdk binding requires sequences in the amino terminus of Cdc18 but does not require the presence of consensus cdk phosphorylation sites. (A) Deletion mutant Cdc18 fusion proteins were purified from fission yeast and equal cell equivalents were assayed for associated histone H1 kinase (Upper). Kinase activity was quantitated and normalized to the amount of activity associated with GSTcdc18 (Lower). (B) The ability of the deletion mutants to rescue cells depleted of wild-type Cdc18 was tested as described in Fig. 1A. (C) Cdc18 fusion protein lacking five cdk consensus phosphorylation sites was affinity-purified and assayed for associated histone H1 kinase activity (Upper). Kinase activity was quantitated as for A (Lower).