title: A mutation in T7 RNA polymerase that facilitates promoter clearance.
abstract: Like multisubunit RNA polymerases (RNAPs), T7 RNAP frequently releases its transcript over the initial 8-12 transcribed nucleotides, when it still contacts the promoter. This abortive cycling, which is most prominent with initial sequences that deviate from those of T7 late genes, eventually compromises productive transcription. Starting from an in vivo situation where transcription of a target gene by T7 RNAP is virtually abolished because of extensive abortive cycling, we have selected a mutation in RNAP that restores target gene expression. In vitro, this mutation (P266L) weakens promoter binding but markedly reduces abortive cycling over a variety of initial sequences by stabilizing the transcription complex at nucleotides 5-8. Other substitutions of P266 have similar effects. X-ray data show that during the transition from initial to elongation complex, the N-terminal region undergoes a major structural switch of which P266 constitutes one of the hinges. How the mutation might facilitate this switch is tentatively discussed. On the practical side, the mutation can significantly improve in vitro transcription, particularly from templates carrying unfavorable initial sequences.
authors.affiliation: Laboratoire de Génétique Moléculaire, Centre National de la Recherche Scientifique UMR8541, Ecole Normale Supérieure, 46 Rue d'Ulm, 75230 Paris Cedex 05, France.
authors.forename: Jean
authors.initials: J
authors.lastname: Guillerez
authors.forename: Pascal J
authors.initials: PJ
authors.lastname: Lopez
authors.forename: Florence
authors.initials: F
authors.lastname: Proux
authors.forename: Hélène
authors.initials: H
authors.lastname: Launay
authors.forename: Marc
authors.initials: M
authors.lastname: Dreyfus
mesh_terms: D019943:Amino Acid Substitution; D017123:Bacteriophage T7 / Q000201:enzymology* / Q000235:genetics; D001483:Base Sequence; D012321:DNA-Directed RNA Polymerases / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010957:Plasmids; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011487:Protein Conformation; D021122:Protein Subunits; D014158:Transcription, Genetic; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D021122:Protein Subunits; D014764:Viral Proteins; C062210:bacteriophage T7 RNA polymerase; D012321:DNA-Directed RNA Polymerases