Figure 4.

Premature phosphorylation of Cdks on tyrosine 15 in embryos expressing exogenous XChk1. Embryos were injected at the one-cell stage with buffer, 15 ng of control mRNA, or 15-ng XChk1 mRNA. Western blots were reacted with an antibody that recognizes the phosphorylated tyrosine 15 epitope of Cdc2 and Cdk2. The equivalent of one embryo is loaded per lane. These results were reproducible in multiple experiments by using different control RNAs. The migration of molecular-weight markers in kDa is shown at the left.