An Rb-Skp2-p27 pathway mediates acute cell cycle inhibition by Rb and is retained in a partial-penetrance Rb mutant.

It is believed that Rb blocks G1-S transition by inhibiting expression of E2F regulated genes. Here, we report that the effects of E2F repression lag behind the onset of G1 cell cycle arrest in timed Rb reexpression experiments. In comparison, kinase inhibitor p27Kip1 protein accumulates with a faster kinetics.