title: Effects of Transcription Elongation Rate and Xrn2 Exonuclease Activity on RNA Polymerase II Termination Suggest Widespread Kinetic Competition.
abstract: The torpedo model of transcription termination asserts that the exonuclease Xrn2 attacks the 5'PO4-end exposed by nascent RNA cleavage and chases down the RNA polymerase. We tested this mechanism using a dominant-negative human Xrn2 mutant and found that it delayed termination genome-wide. Xrn2 nuclease inactivation caused strong termination defects downstream of most poly(A) sites and modest delays at some histone and U snRNA genes, suggesting that the torpedo mechanism is not limited to poly(A) site-dependent termination. A central untested feature of the torpedo model is that there is kinetic competition between the exonuclease and the pol II elongation complex. Using pol II rate mutants, we found that slow transcription robustly shifts termination upstream, and fast elongation extends the zone of termination further downstream. These results suggest that kinetic competition between elongating pol II and the Xrn2 exonuclease is integral to termination of transcription on most human genes.
authors.affiliation: Deptartment of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, PO Box 6511, Aurora, CO 80045, USA.
authors.forename: Nova
authors.initials: N
authors.lastname: Fong
authors.affiliation: Deptartment of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, PO Box 6511, Aurora, CO 80045, USA.
authors.forename: Kristopher
authors.initials: K
authors.lastname: Brannan
authors.affiliation: Deptartment of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, PO Box 6511, Aurora, CO 80045, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Erickson
authors.affiliation: Deptartment of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, PO Box 6511, Aurora, CO 80045, USA.
authors.forename: Hyunmin
authors.initials: H
authors.lastname: Kim
authors.affiliation: Deptartment of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, PO Box 6511, Aurora, CO 80045, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Cortazar
authors.affiliation: Deptartment of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, PO Box 6511, Aurora, CO 80045, USA.
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Sheridan
authors.affiliation: Deptartment of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, PO Box 6511, Aurora, CO 80045, USA.
authors.forename: Tram
authors.initials: T
authors.lastname: Nguyen
authors.affiliation: Deptartment of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, PO Box 6511, Aurora, CO 80045, USA.
authors.forename: Shai
authors.initials: S
authors.lastname: Karp
authors.affiliation: Deptartment of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, PO Box 6511, Aurora, CO 80045, USA. Electronic address: david.bentley@ucdenver.edu.
authors.forename: David L
authors.initials: DL
authors.lastname: Bentley
mesh_terms: D002460:Cell Line; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D005095:Exoribonucleases / Q000235:genetics* / Q000378:metabolism; D015894:Genome, Human; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008214:Lymphocytes / Q000166:cytology / Q000378:metabolism; D008957:Models, Genetic; D009154:Mutation; D011061:Poly A / Q000235:genetics* / Q000378:metabolism; D012319:RNA Polymerase II / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D061805:Transcription Elongation, Genetic; D061806:Transcription Termination, Genetic
chemical_list: D012333:RNA, Messenger; D011061:Poly A; D012319:RNA Polymerase II; D005095:Exoribonucleases; C120903:XRN2 protein, human