Into and out of G1: the control of cell proliferation.

Progression of cells through G1 is an orderly process which is regulated by a series of key proteins. Over the past few years a number of these proteins have been identified and their mode of action has been studied in detail. This review will concentrate on the current knowledge about the function in G1 of cyclins, cyclin dependent kinases, the retinoblastoma protein and other related 'pocket' proteins. Mutations or deregulation of some of these proteins confer a growth advantage and their role in malignant transformation will be discussed.