Control and activity of type-1 serine/threonine protein phosphatase during the cell cycle.

The first part of this discourse will serve as a compendium of selected aspects of PP1 activity and control during the cell cycle. The latter sections will focus on the mammalian cell cycle dependent activity of PP1 on the negative growth regulatory product of the retinoblastoma susceptibility gene, pRB. The purpose here is to suggest one possible mechanism to explain how this phosphatase can effect cell cycle progression. An argument is made for PP1 playing an indirect role in regulating cell cycle progression by modulating the growth suppressive activity of pRB.