Cell cycle-dependent protein expression of mammalian homologs of yeast DNA double-strand break repair genes Rad51 and Rad52

Abstract Recently, human and rodent homologs of yeast repair genes Rad51 and Rad52 have been identified and proposed to play roles in DNA double-strand break (DSB) repair. In this study, cell cycle-dependent expression of human and rodent RAD51 and RAD52 proteins was monitored using two approaches. First, flow cytometric measurements of DNA content and immunofluorescence were used to determine the phase-specific levels of RAD51 and RAD52 protein expression in irradiated and control populations. The expression of both proteins was lowest in G 0 /G 1 , increased in S and reached a maximum in G 2 /M. No difference was found in the whole-cell level of RAD51 or RAD52 protein expression between γ-irradiated and control cell populations. Second, cell cycle-dependent protein expression was confirmed by Western analysis of populations synchronized in G 0 , G 1 and G 2 phases. Analysis of V3, a hamster equivalent of SCID, indicates that the protein level increases of RAD51 and RAD52 from G 0 to G 1 /S/G 2 do not require DNA–PK.