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

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 G₀/G₁, increased in S and reached a maximum in G₂/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 G₀, G₁ and G₂ phases. Analysis of V3, a hamster equivalent of SCID, indicates that the protein level increases of RAD51 and RAD52 from G₀ to G₁/S/G₂ do not require DNA-PK.