Fig. 2. Role of p300/CBP during cell cycle progression. The diagram describes the role of p300 in regulating the activity of the cell cycle transcription factor E2F. Phosphorylation of pRb by cyclin-D-CDK4 kinase releases pRb from E2F, thereafter facilitating the activation of E2F-target genes. Subsequent phosphorylation of a CDK site by cyclin-E-CDK2 in the transactivation domain of E2F augments the interaction with p300, thereafter leading to the increased transcriptional activity of E2F-target genes.