Interaction of a transcriptional repressor with the RNA polymerase II holoenzyme plays a crucial role in repression

The yeast transcriptional repressor Tup1, tethered to DNA, represses to str ikingly different degrees transcription elicited by members of two classes of activators. Repression in both cases is virtually eliminated by mutation of either member of the cyclin-kinase pair Srb10/11. In contrast, telomeri c chromatin affects both classes of activators equally, and in neither case is that repression affected by mutation of Srb10/11. In vitro, Tup1 intera cts with RNA polymerase II holoenzyme bearing Srb10 as well as with the sep arated Srb10. These and other findings indicate that at least one aspect of Tup1's action involves interaction with the RNA polymerase II holoenzyme.