Analyzing RB and E2F during the G1-S transition.

The G1/S-phase restriction point is an important landmark in the mammalian cell division cycle. The key regulator of the G1/S transition is the retinoblastoma gene product (pRB). It prevents the transcription of genes required for S-phase progression by repressing E2F transcription factors. An increase in Cdk phosphorylation of pRB causes the release of E2F transcription factors and advancement into S phase. Here we describe two simple techniques used to assess pRB phosphorylation and E2F transcription during G1/S progression.