Efficient termination of transcription by RNA polymerase I requires the 5' exonuclease Rat1 in yeast.
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.
El Hage
Aziz
A
Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh EH9 3JR, United Kingdom.
Koper
Michal
M
Kufel
Joanna
J
Tollervey
David
D
D004275:DNA, Ribosomal / Q000378:metabolism; D005095:Exoribonucleases / Q000378:metabolism*; D008954:Models, Biological; D008957:Models, Genetic; D009687:Nuclear Proteins / Q000378:metabolism; D012318:RNA Polymerase I / Q000378:metabolism*; D012340:RNA, Ribosomal, 5.8S / Q000378:metabolism; D016601:RNA-Binding Proteins; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D013728:Terminator Regions, Genetic / Q000235:genetics*; D014158:Transcription, Genetic
D004275:DNA, Ribosomal; D009687:Nuclear Proteins; D012340:RNA, Ribosomal, 5.8S; D016601:RNA-Binding Proteins; C473024:Rai1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C075577:RAT1 protein, S cerevisiae; D012318:RNA Polymerase I; D005095:Exoribonucleases; C068398:XRN1 protein, S cerevisiae