title: Divergent contributions of conserved active site residues to transcription by eukaryotic RNA polymerases I and II.
abstract: Multisubunit RNA polymerases (msRNAPs) exhibit high sequence and structural homology, especially within their active sites, which is generally thought to result in msRNAP functional conservation. However, we show that mutations in the trigger loop (TL) in the largest subunit of RNA polymerase I (Pol I) yield phenotypes unexpected from studies of Pol II. For example, a well-characterized gain-of-function mutation in Pol II results in loss of function in Pol I (Pol II: rpb1- E1103G; Pol I: rpa190-E1224G). Studies of chimeric Pol II enzymes hosting Pol I or Pol III TLs suggest that consequences of mutations that alter TL dynamics are dictated by the greater enzymatic context and not solely the TL sequence. Although the rpa190-E1224G mutation diminishes polymerase activity, when combined with mutations that perturb Pol I catalysis, it enhances polymerase function, similar to the analogous Pol II mutation. These results suggest that Pol I and Pol II have different rate-limiting steps.
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Birmingham, AL 35294-0024, USA.
authors.forename: Olga V
authors.initials: OV
authors.lastname: Viktorovskaya
authors.forename: Krysta L
authors.initials: KL
authors.lastname: Engel
authors.forename: Sarah L
authors.initials: SL
authors.lastname: French
authors.forename: Ping
authors.initials: P
authors.lastname: Cui
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Vandeventer
authors.forename: Emily M
authors.initials: EM
authors.lastname: Pavlovic
authors.forename: Ann L
authors.initials: AL
authors.lastname: Beyer
authors.forename: Craig D
authors.initials: CD
authors.lastname: Kaplan
authors.forename: David A
authors.initials: DA
authors.lastname: Schneider
mesh_terms: D000595:Amino Acid Sequence; D020134:Catalytic Domain; D017124:Conserved Sequence; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D012318:RNA Polymerase I / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D012319:RNA Polymerase II / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D012319:RNA Polymerase II; D012318:RNA Polymerase I