Competitive recruitment of CBP and Rb-HDAC regulates UBF acetylation and ribosomal transcription

RNA polymerase I (Poll) transcription is activated by the HMG box architect ural factor UBF, which loops approximately 140 bp of DNA into the enhanceso me, necessitating major chromatin remodeling. Here we show that the acetylt ransferase CBP is recruited to and acetylates UBF both in vitro and in vivo . CBP activates Poll transcription in vivo through its acetyltransferase do main and acetylation of UBF facilitates transcription derepression and acti vation in vitro. CBP activation and Rb suppression of ribosomal transcripti on by recruitment to UBF are mutually exclusive, regulating in vivo Poll tr anscription through an acetylation-deacetylation "flip-flop." Thus, Poll tr anscription is regulated by protein acetylation, and the competitive recrui tment of CBP and Rb.