Yeast RNase III triggers polyadenylation-independent transcription termination

Transcription termination of messenger RNA (mRNA) is normally achieved by polyadenylation followed by Rat1p-dependent 5'-3' exoribonuleolytic degradation of the downstream transcript. Here we show that the yeast ortholog of the dsRNA-specific ribonuclease III (Rnt1p) may trigger Rat1p-dependent termination of RNA transcripts that fail to terminate near polyadenylation signals. Rnt1p cleavage sites were found downstream of several genes, and the deletion of RNT1 resulted in transcription readthrough. Inactivation of Rat1p impaired Rnt1p-dependent termination and resulted in the accumulation of 3' end cleavage products. These results support a model for transcription termination in which cotranscriptional cleavage by Rnt1p provides access for exoribonucleases in the absence of polyadenylation signals.

This work was supported by a grant from the Canadian Institute of Health Research. S. A. is a Chercheur Boursier National of the Fonds de la Recherche en Santé du Québec. F.R. holds a New Investigator Award from the Canadian Institute of Health Research. P-É.J. holds a post-doctoral award from the IRCM training program in cancer research funded by the CIHR. J.-R.L is a research fellow of the Terry Fox Foundation through an award from the National Cancer Institute of Canada.