Retinoblastoma protein and anaphase-promoting complex physically interact and functionally cooperate during cell-cycle exit.

The retinoblastoma protein (pRB) negatively regulates the progression from G1 to S phase of the cell cycle, in part, by repressing E2F-dependent transcription. pRB also possesses E2F-independent functions that contribute to cell-cycle control--for example, during pRB-mediated cell-cycle arrest pRB associates with Skp2, the F-box protein of the Skp1-Cullin-F-box protein (SCF) E3 ubiquitin ligase complex, and promotes the stability of the cyclin-dependent kinase-inhibitor p27(Kip1) through an unknown mechanism. Degradation of p27(Kip1) is mediated by ubiquitin-dependent targeting of p27(Kip1) by SCF -Skp2 (ref.

The retinoblastoma protein regulates pericentric heterochromatin.

The retinoblastoma protein (pRb) has been proposed to regulate cell cycle progression in part through its ability to interact with enzymes that modify histone tails and create a repressed chromatin structure. We created a mutation in the murine Rb1 gene that disrupted pRb's ability to interact with these enzymes to determine if it affected cell cycle control. Here, we show that loss of this interaction slows progression through mitosis and causes aneuploidy.

Lytic cycle gene regulation of Epstein-Barr virus.

Episomal reporter plasmids containing the Epstein-Barr virus (EBV) oriP sequence stably transfected into Akata Burkitt's lymphoma cells were used to analyze EBV lytic cycle gene regulation. First, we found that the Zp promoter of EBV, but not the Rp promoter, can be activated in the absence of protein synthesis in these oriP plasmids, casting doubt on the immediate early status of Rp. An additional level of regulation of Zp was implied by analysis of a mutation of the ZV element.

Native E2F/RBF complexes contain Myb-interacting proteins and repress transcription of developmentally controlled E2F target genes.

The retinoblastoma tumor suppressor protein (pRb) regulates gene transcription by binding E2F transcription factors. pRb can recruit several repressor complexes to E2F bound promoters; however, native pRb repressor complexes have not been isolated. We have purified E2F/RBF repressor complexes from Drosophila embryo extracts and characterized their roles in E2F regulation.

p55, the Drosophila ortholog of RbAp46/RbAp48, is required for the repression of dE2F2/RBF-regulated genes.

Many proteins have been proposed to be involved in retinoblastoma protein (pRB)-mediated repression, but it is largely uncertain which cofactors are essential for pRB to repress endogenous E2F-regulated promoters. Here we have taken advantage of the stream-lined Drosophila dE2F/RBF pathway, which has only two E2Fs (dE2F1 and dE2F2), and two pRB family members (RBF1 and RBF2). With RNA interference (RNAi), we depleted potential corepressors and looked for the elevated expression of groups of E2F target genes that are known to be directly regulated by RBF1 and RBF2.

Promoter sequences required for reactivation of Epstein-Barr virus from latency.

A luciferase reporter system with stably transfected oriP plasmids in Akata Burkitt's lymphoma cells provides a quantitative assay for the BZLF1 Zp promoter in response to B-cell receptor (BCR) activation by cross-linking with anti-immunoglobulin. In this system, detailed kinetic studies of promoter activity are possible. Previously reported promoter elements upstream of -221 from the transcription start and the ZIIR sequence had little effect on the Zp promoter, but the ZI and ZIIIA elements were essential for early activation.