title: Two distinct modes of RecA action are required for DNA polymerase V-catalyzed translesion synthesis.
abstract: SOS mutagenesis in Escherichia coli requires DNA polymerase V (pol V) and RecA protein to copy damaged DNA templates. Here we show that two distinct biochemical modes for RecA protein are necessary for pol V-catalyzed translesion synthesis. One RecA mode is characterized by a strong stimulation in nucleotide incorporation either directly opposite a lesion or at undamaged template sites, but by the absence of lesion bypass. A separate RecA mode is necessary for translesion synthesis. The RecA1730 mutant protein, which was identified on the basis of its inability to promote pol V (UmuD'(2)C)-dependent UV-mutagenesis, appears proficient for the first mode of RecA action but is deficient in the second mode. Data are presented suggesting that the two RecA modes are "nonfilamentous". That is, contrary to current models for SOS mutagenesis, formation of a RecA nucleoprotein filament may not be required for copying damaged DNA templates. Instead, SOS mutagenesis occurs when pol V interacts with two RecA molecules, first at a 3' primer end, upstream of a template lesion, where RecA mode 1 stimulates pol V activity, and subsequently at a site immediately downstream of the lesion, where RecA mode 2 cocatalyzes lesion bypass. We posit that in vivo assembly of a RecA nucleoprotein filament may be required principally to target pol V to a site of DNA damage and to stabilize the pol V-RecA interaction at the lesion. However, it is only a RecA molecule located at the 3' filament tip, proximal to a damaged template base, that is directly responsible for translesion synthesis.
authors.affiliation: Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089-1340, USA.
authors.forename: Phuong
authors.initials: P
authors.lastname: Pham
authors.forename: Erica M
authors.initials: EM
authors.lastname: Seitz
authors.forename: Sergei
authors.initials: S
authors.lastname: Saveliev
authors.forename: Xuan
authors.initials: X
authors.lastname: Shen
authors.forename: Roger
authors.initials: R
authors.lastname: Woodgate
authors.forename: Michael M
authors.initials: MM
authors.lastname: Cox
authors.forename: Myron F
authors.initials: MF
authors.lastname: Goodman
mesh_terms: D002384:Catalysis; D004261:DNA Replication / Q000502:physiology*; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins; D007700:Kinetics; D011938:Rec A Recombinases / Q000378:metabolism*; D013379:Substrate Specificity; D013698:Templates, Genetic
chemical_list: D029968:Escherichia coli Proteins; D011938:Rec A Recombinases; C120926:DNA polymerase V, E coli; D004259:DNA-Directed DNA Polymerase