The transcript release factor PTRF augments ribosomal gene transcription by facilitating reinitiation of RNA polymerase I

Termination of murine rDNA transcription by RNA polymerase I(Pol I) require s pausing of Pol I by terminator-bound TTF-l (transcription termination fac tor for Pol I), followed by dissociation of the ternary complex by PTRF (Po l I and transcript release factor), To examine the functional correlation b etween transcription termination and initiation, we have compared transcrip tion on terminator-containing and terminator-less rDNA templates. We demons trate that terminated RNA molecules are more efficiently synthesized than r un-off transcripts, indicating that termination facilitates reinitiation, T ranscriptional enhancement is observed in multiple-but not single-round tra nscription assays measuring either promoter-dependent or promoter-independe nt pol I transcription, Increased synthesis of terminated transcripts is ob served in crude extracts but not in a PTRF-free reconstituted transcription system, indicating that PTRF-mediated release of pre-rRNA is responsible f or transcriptional enhancement, Consistent with PTRF serving an important r ole in modulating the efficiency of rRNA synthesis, PTRF exhibits pronounce d charge heterogeneity, is phosphorylated at multiple sites and fractionate s into transcriptionally active and inactive forms. The results suggest tha t regulation of PTRF activity may be an as yet unrecognized means to contro l the efficiency of ribosomal RNA synthesis.