Transcription factor E2F1
nucleus
The interaction of RB with E2F coincides with an inhibition of the transcriptional activity of E2F.
Recent experiments have shown that the E2F transcription factor is in a complex with the RB1 gene product. The E2F-pRB complex can be reconstituted in an in vitro assay using a GST-RB fusion protein isolated from Escherichia coli. This interaction is dependent on pRB sequences involved in E1A/T-antigen binding as well as carboxy-terminal pRB sequences that are not necessary for E1A/T binding. Moreover, reconstitution assays reveal a requirement for an accessory factor, in addition to E2F and pRB, for formation of the E2F-pRB complex. Assays of transcription from the adenovirus E2 promoter in transfection experiments demonstrate that formation of the complex containing pRB and E2F coincides with an inhibition of E2F-dependent transcriptional activity. A mutant pRB protein that does not associate with E2F does not inhibit transcription. We conclude that as a consequence of its interaction with E2F, pRB may regulate the transcriptional function of the E2F factor.