PARENT SESSION
9:00 AM to 11:00 AM
Tuesday, April 23, 2002
Symposium 18
Double-strand Break Repair by Homologous Recombinations
Room: Nevada 4-5
Chair: Powell, Simon11
Speakers: Sung, Patrick2; Jasin, Maria3; Powell, Simon1231
(S18-3) Interactions involving the Rad51 paralogs Rad51C and XRCC3 in human cells.
Schild, David*,1, Wiese, Claudia1, Collins, David1, Kronenberg, Amy1, 1 Lawrence Berkeley Natl. Lab., Berkeley, CA
ABSTRACT-
Homologous recombinational repair of DNA double-strand breaks and crosslinks in human cells is likely to require Rad51 and the five Rad51 paralogs (XRCC2, XRCC3, Rad51B/Rad51L1, Rad51C/Rad51L2 and Rad51D/Rad51L3), as has been shown in chicken and rodent cells. These Rad51 paralogs share 20-30% sequence identity with Rad51 and with each other, and probably assist Rad51 in displacing RPA from ssDNA during an early step in recombinational repair, as has been shown for the yeast Rad51 paralogs. Previously, we reported on the interactions among the human Rad51 paralogs using baculovirus and two- and three-hybrid yeast systems. To test for interactions involving XRCC3 and Rad51C in human cells, stable cell lines have been isolated that express (His)6-tagged versions of XRCC3 or Rad51C. Ni++-binding experiments demonstrate that XRCC3 and Rad51C interact in human cells. In addition, we find that Rad51C, but not XRCC3, interacts directly or indirectly with Rad51B, Rad51D and XRCC2. These results argue that there are at least two complexes of Rad51 paralogs in human cells (Rad51C-XRCC3 and Rad51B-Rad51C-Rad51D-XRCC2), both containing Rad51C. Moreover, Rad51 is not found in these complexes. X-ray treatment did not alter either the level of any Rad51 paralog, or the observed interactions between paralogs. However, the endogenous level of Rad51C is moderately elevated in the XRCC3-overexpressing cell line, suggesting that dimerization between these proteins might help stabilize Rad51C. Our finding of at least two protein complexes, both containing Rad51C, suggests that there might be a type of hand-off or exchange reaction occurring between these complexes during recombinational repair in human cells.
KEYWORDS: Rad51 paralogs, Protein interactions, recombinational repair