title: Involvement of Rad51C in two distinct protein complexes of Rad51 paralogs in human cells.
abstract: Genetic studies in rodent and chicken mutant cell lines have suggested that Rad51 paralogs (XRCC2, XRCC3, Rad51B/Rad51L1, Rad51C/Rad51L2 and Rad51D/Rad51L3) play important roles in homologous recombinational repair of DNA double-strand breaks and in maintaining chromosome stability. Previous studies using yeast two- and three-hybrid systems have shown interactions among these proteins, but it is not clear whether these interactions occur simultaneously or sequentially in vivo. By utilizing immunoprecipitation with extracts of human cells expressing epitope-tagged Rad51 paralogs, we demonstrate that XRCC2 and Rad51D, while stably interacting with each other, co-precipitate with Rad51C but not with XRCC3. In contrast, Rad51C is pulled down with XRCC3, whereas XRCC2 and Rad51D are not. In addition, Rad51B could be pulled down with Rad51C and Rad51D, but not with XRCC3. These results suggest that Rad51C is involved in two distinct in vivo complexes: Rad51B-Rad51C-Rad51D-XRCC2 and Rad51C-XRCC3. In addition, we demonstrate that Rad51 co-precipitates with XRCC3 but not with XRCC2 or Rad51D, suggesting that Rad51 can be present in an XRCC3-Rad51C-Rad51 complex. These complexes may act as functional units and serve accessory roles for Rad51 in the presynapsis stage of homologous recombinational repair.
authors.affiliation: Biology and Biotechnology Research Program, L441, Lawrence Livermore National Laboratory, PO Box 808, Livermore, CA 94551-0808, USA. liu3@llnl.gov
authors.forename: Nan
authors.initials: N
authors.lastname: Liu
authors.forename: David
authors.initials: D
authors.lastname: Schild
authors.forename: Michael P
authors.initials: MP
authors.lastname: Thelen
authors.forename: Larry H
authors.initials: LH
authors.lastname: Thompson
mesh_terms: D000818:Animals; D030161:Avian Proteins; D002460:Cell Line; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D005720:Gamma Rays; D006367:HeLa Cells; D006801:Humans; D046911:Macromolecular Substances; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D011233:Precipitin Tests; D051135:Rad51 Recombinase; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014162:Transfection
chemical_list: D030161:Avian Proteins; D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; C413002:RAD51B protein, human; C448305:RAD51C protein, human; C112629:RAD51D protein, human; D011993:Recombinant Fusion Proteins; C110901:X-ray repair cross complementing protein 3; C113187:XRCC2 protein, human; C495150:RAD51 protein, Gallus gallus; C495153:RAD51 protein, human; D051135:Rad51 Recombinase