Fig. 4. CDK protein content in liver nuclear extracts. In A, nuclear extracts prepared from livers of various developmental ages were analyzed by Western blot for CDK4. The result shown was replicated in a second, independent experiment. In B, parallel analyses were done for CDK6 using IP followed by Western immunoblot. Upper panel, densitometric analysis of the autoradiogram shown in the lower panel. Error bars, SE; C1, no antibody control. Similar results were obtained in two replicate experiments.