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1: Genes Dev. 2008 Apr 15;22(8):1069-81.
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Efficient termination of transcription by RNA polymerase I requires the 5' exonuclease Rat1 in yeast.

El Hage A, Koper M, Kufel J, Tollervey D.

Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh EH9 3JR, United Kingdom.

During transcription termination by RNA polymerase II on protein-coding genes, the nuclear 5' exonuclease Rat1/Xrn2 degrades the nascent transcript downstream from the polyadenylation site and "torpedoes" the polymerase. We report that the activity of Rat1 is also required for efficient termination by RNA polymerase I (Pol I) on the rDNA. In strains lacking catalytically active Rat1 or its cofactor Rai1, Pol I reads through the major, "Reb1-dependent" terminator (T1) but stops downstream at the "fail-safe" terminator (T2) and replication fork barrier (RFB). The absence of both Rat1 and the RFB-binding protein Fob1 increased Pol I read-through of T2 and the RFB. We propose that cotranscriptional cleavage of the pre-rRNA by the endonuclease Rnt1 generates a loading site for the Rat1/Rai1 complex, which then degrades the nascent transcript. When Rat1 catches Pol I, which is predicted to be paused at T1, transcription is terminated.

Publication Types:
PMID: 18413717 [PubMed - indexed for MEDLINE]

PMCID: PMC2335327