Rb interacts with TAF_II250/TFIID through multiple domains

Abstract

The retinoblastoma tumor suppressor gene product (Rb) binds directly to the largest TFIID subunit, TATA-binding protein associated factor TAF_II250, first identified as the cell cycle regulatory protein CCG1. Here we map the domains in Rb and TAF_II250 important for their interaction in vitro and in vivo. Both the amino terminus and the large pocket of Rb are able to associate independently with TAF_II250. The binding domain(s) within the large pocket are distinct from the viral oncoprotein and E2F binding region since certain pocket mutations, which abolish E1A binding, do not abolish TAF_II250 binding. Consistent with the large pocket of Rb binding to TAF_II250, the large pocket domains of both p107 and p130 are able to bind to TAF_II250 in vivo. We also demonstrate that at least two regions of TAF_II250 are able to bind to the large pocket of Rb independently whereas the amino terminus of Rb binds to a distinct domain in TAF_II250. We further demonstrate that Rb can bind to TFIID in vitro, presumably in part through an interaction with TAF_II250. Our results suggest a complex interaction between Rb and TAF_II250 and imply that TAF_II250, TFIID, and potentially other basal transcription factors are targets for regulation by Rb and Rb-related proteins.