Fig. 1. Activation of H1 kinase activity by overexpression of cyclins and cdk2. RNA encoding cyclin E alone or with cdk2, cyclin A2 alone or with cdk2, or cdk2 alone were injected into fertilised eggs and allowed to develop until stage 8. Cdk2 was immunoprecipitated from injected embryos (lanes as labelled) and tested for its ability to phosphorylate histone H1.