title: Implication of DNA polymerase lambda in alignment-based gap filling for nonhomologous DNA end joining in human nuclear extracts.
abstract: Accurate repair of free radical-mediated DNA double-strand breaks by the nonhomologous end joining pathway requires replacement of fragmented nucleotides in the aligned ends by a gap-filling DNA polymerase. Nuclear extracts of human HeLa cells, supplemented with recombinant XRCC4-DNA ligase IV complex (XRCC4/ligase IV), were capable of accurately rejoining model double-strand break substrates with a 1- or 2-base gap, and the gap-filling step was dependent on XRCC4/ligase IV. To determine what polymerase was responsible for gap filling, end joining was examined in the presence of polyclonal antibodies against each of two prime candidate enzymes, DNA polymerases mu and lambda, both of which were present in the extracts. For a DNA substrate with partially complementary 3' overhangs and a 2-base gap, antibodies to polymerase lambda completely eliminated both gap filling and accurate end joining, whereas antibodies to polymerase mu had little effect. Immunodepletion of polymerase lambda, but not polymerase mu, likewise blocked both gap filling and end joining, and both functions could be restored by addition of recombinant polymerase lambda. Recombinant polymerase mu, and a truncated polymerase lambda lacking the Brca1 C-terminal domain, were at least 10-fold less active in restoring gap filling to the immunodepleted extracts, and polymerase beta was completely inactive. The results suggest that polymerase lambda is the primary gap-filling polymerase for accurate nonhomologous end joining, and that the Brca1 C-terminal domain is required for this activity.
authors.affiliation: Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia 23298, USA.
authors.forename: Jae Wan
authors.initials: JW
authors.lastname: Lee
authors.forename: Luis
authors.initials: L
authors.lastname: Blanco
authors.forename: Tong
authors.initials: T
authors.lastname: Zhou
authors.forename: Miguel
authors.initials: M
authors.lastname: Garcia-Diaz
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Bebenek
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Kunkel
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Wang
authors.forename: Lawrence F
authors.initials: LF
authors.lastname: Povirk
mesh_terms: D001483:Base Sequence; D002467:Cell Nucleus / Q000201:enzymology*; D004247:DNA / Q000235:genetics* / Q000378:metabolism; D019951:DNA Polymerase beta / Q000737:chemistry* / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D013379:Substrate Specificity
chemical_list: D004268:DNA-Binding Proteins; C101467:XRCC4 protein, human; D004247:DNA; C415367:DNA polymerase beta2; D019951:DNA Polymerase beta