Figure 7.

Model for in vivo occupancy by E2F and pRB family members during cell cycle progression. (A) In vivo occupation of E2F-1, Cdc25A, cyclin A, Cdc6, and p107 promoters by the E2F and pRB family during cell cycle progression and transcriptional consequences. (B) In vivo binding of B-myb promoter. In A and B, promoter binding by E2F-4 correlates with transcriptional repression, whereas binding by E2F-1 and E2F-3 occurs at a time when each promoter is activated. However, the B-myb promoter is transcriptionally active after E2F is no longer bound, consistent with Zwicker et al. (1996). (D) HDAC activity; (H) nucleosomes; (Ac) acetylated histones; (HAT) histone acetyltransferase. These promoters are likely to be regulated by additional trans-activator proteins proximal to E2F, including Sp1. Recruitment of deacetylase and HAT activities could occur by direct interactions with E2F complexes or could require additional factors (X) yet to be defined.