RNA polymerase I from S. cerevisiae depends on an additional factor to release terminated transcripts from the template

Terminated transcripts were generated at the ends of linearized DNA templates and at DNA-bound lac repressor by in vitro transcription with highly enriched or purified yeast RNA polymerase I (pol I). The release of the synthesized transcripts from the DNA was analyzed using immobilized DNA as template for the transcription reaction. An additional activity distinguishable from pol I was necessary to remove the terminated RNA from the template. Efficiency of transcript release could be improved if a thymidine-rich DNA fragment was located upstream of the transcriptional arrest caused by the DNA-bound lac repressor. The release activity interacted with different forms of polymerases, pol I able to initiate on the ribosomal gene promoter and pol I only active in non-specific transcription.