THE RETINOBLASTOMA SUSCEPTIBILITY GENE-PRODUCT REPRESSES TRANSCRIPTION WHEN DIRECTLY BOUND TO THE PROMOTER

Rb represses E2F-mediated transcription in part by blocking the trans- activation domain of E2F. In addition, Rb can convert an E2F binding s ite from a positive to a negative element. To examine the effect of a Rb-DNA bound complex on transcription, full-length Rb was fused to the DNA binding domain of GAL4. Here, we report that GAL4-Rb can repress transcription mediated by either Sp1, AP-1, or p53, dependent upon the presence of both the GAL4 DNA binding domain and GAL4 binding sites. Moreover, GAL4-Rb inhibited the activity of the herpes simplex virus t k promoter from GAL4 binding sites located at a distance from the prom oter. In contrast, GAL4-Rb was unable to repress basal transcription. Cotransfection of specific cyclins and cyclin dependent kinases or SV4 0 T-antigen abolished the repressive activity of GAL4-Rb. The domains of Rb involved in mediating the repression of transcription were mappe d to regions that are overlapping, but not identical, to those require d for the interaction with E2F. We propose that Rb can function as a g eneral repressor of transcription when bound to the promoter region.