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  • Title: Efficient termination of transcription by RNA polymerase I requires the 5' exonuclease Rat1 in yeast.
    Author: El Hage A, Koper M, Kufel J, Tollervey D.
    Journal: Genes Dev; 2008 Apr 15; 22(8):1069-81. PubMed ID: 18413717.
    Abstract:
    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.
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