Mechanism of transcription termination: PTRF interacts with the largest subunit of RNA polymerase I and dissociates paused transcription complexes from yeast and mouse

Transcription termination by RNA polymerase I (Pol I) is a stepwise process . First the elongating RNA polymerase is forced to pause by DNA-bound trans cription termination factor (TTF-I). Then the ternary transcription complex is dissociated by PTRF, a novel factor that promotes release of both nasce nt transcripts and Pol I from the template. In this study we have investiga ted the ability of PTRF to liberate transcripts from ternary transcription complexes isolated from yeast and mouse;Using immobilized, tailed templates that contain terminator sequences from Saccharomyces cerevisiae and mouse, respectively, we demonstrate that PTRF -promotes release of terminated tra nscripts, irrespective of whether mouse Pol I has interacted with the murin e termination factor TTF-I or its yeast homolog Reb1p. In contrast, mouse P ol I paused by the lac repressor remains bound to the template both in the presence and absence of PTRF. We demonstrate that PTRF interacts with the l argest subunit of murine Pol I, with TTF-I and Reb1p, but not the lac repre ssor. The results imply that Pol I transcription termination in yeast and m ouse is mediated by conserved interactions between Pol I, Reb1p/TTF-I and P TRF.