Co-transcriptional RNA cleavage provides a failsafe termination mechanism for yeast RNA polymerase I.
Ribosomal RNA, transcribed by RNA polymerase (Pol) I, accounts for most cellular RNA. Since Pol I transcribes rDNA repeats with high processivity and polymerase density, transcription termination is a critical process. Early in vitro studies proposed polymerase pausing by Reb1 and transcript release at the T-rich element T1 determined transcription termination. However recent in vivo studies revealed a 'torpedo' mechanism for Pol I termination: co-transcriptional RNA cleavage by Rnt1 provides an entry site for the 5'-3' exonuclease Rat1 that degrades Pol I-associated transcripts destabilizing the transcription complex. Significantly Rnt1 inactivation in vivo reveals a second co-transcriptional RNA cleavage event at T1 which provides Pol I with an alternative termination pathway. An intact Reb1-binding site is also required for Rnt1-independent termination. Consequently our results reconcile the original Reb1-mediated termination pathway as part of a failsafe mechanism for this essential transcription process.
Sir William Dunn School of Pathology, University of Oxford, Oxford, OX1 3RE, UK.
Priscilla
P
Braglia
Junya
J
Kawauchi
Nick J
NJ
Proudfoot
D004265:DNA Helicases / Q000378:metabolism; D004275:DNA, Ribosomal / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000378:metabolism; D005095:Exoribonucleases / Q000378:metabolism; D017353:Gene Deletion; D016296:Mutagenesis; D020365:RNA Helicases / Q000378:metabolism; D012318:RNA Polymerase I / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000096:biosynthesis / Q000378:metabolism*; D043244:Ribonuclease III / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D013728:Terminator Regions, Genetic; D013941:Thymine / Q000032:analysis; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic
D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; C065681:REB1 protein, S cerevisiae; D012335:RNA, Ribosomal; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; C065039:RNA, ribosomal, 25S; C075577:RAT1 protein, S cerevisiae; D012318:RNA Polymerase I; D005095:Exoribonucleases; C468367:RNT1 protein, S cerevisiae; D043244:Ribonuclease III; C542347:SEN1 protein, S cerevisiae; D004265:DNA Helicases; D020365:RNA Helicases; D013941:Thymine