Binding and catalytic properties of the Cdc2 and Crp proteins of Dictyostelium

Dictyostelium expresses at least two proteins of the cyclin-dependent kinas e (Cdk) family, Cdc2 and Crp. Cdc2 levels remain relatively constant during differentiation, whereas the levels of Crp increase dramatically as differ entiation progresses. Crp is highly related to the mammalian Cdk5, and p25 (a truncated form of p35, the activating subunit of Cdk5 from mammalian bra in) stimulates the histone H1 kinase activity of GST-Crp by several fold. I n contrast, p25 does not stimulate the histone H1 kinase activity of GST-Cd c2 or the Cdc2 activity present in cell extracts from vegetative Dictyostel ium cells. GST-Cdc2, in vitro translated Cdc2 and Cdc2 from all stages of d ifferentiation bind to p13(suc1). In contrast, GST-Crp, in vitro translated Crp and the Crp protein present in cell extracts do not bind to p13(suc1) We have confirmed a previous report by Arakane and Maeda [J. Plant Res. (19 97) 110, 81-85] that there is a peak of p13(suc1) bound histone H1 kinase a ctivity during late development, but we found that there was no correspondi ng peak of p13(suc1) bound Cdc2 protein that corresponds to this activity. Taken together, these data suggest that neither Cdc2 nor Crp is responsible for the late developmental peak of histone H1 kinase activity that binds t o p13(suc1).