THE HUMAN REC2 RAD51B GENE ACTS AS A DNA-DAMAGE SENSOR BY INDUCING G(1) DELAY AND HYPERSENSITIVITY TO ULTRAVIOLET-IRRADIATION/

HsRec2/Rad51B is a 350-amino acid protein with a molecular mass of 38, 300 Da that appears to be involved in cell cycle regulation and UV-ind uced apoptosis. The mouse and human genes were isolated based on their homology to a recombinational repair gene from Ustilago maydis and co ntain functional domains to hRAD51 and hLIiM 15 (M. C. Rice et at, Pro c. Natl. Acad. Sci. USA, 94: 7417-7422, 1997), Here, we report the res ults of studies on the behavior of CHO cells containing a plasmid enco ding a wild-type hsRec2/Rad51B, a full-length protein with a single mu tation at residue 163, which lies in the putative src site, and a trun cated version of hsRec2/Rad51B, containing only the first 100 amino ac ids at the NH2 terminus. Using fluorescence-activated cell sorting ana lysis to follow the progression of cells through the cell cycle, we fm d that stable transfectants constitutively overexpressing the wild-typ e human Rec2/Rad51B protein exhibit a G(1) delay. In addition, when ir radiated with UV at a dose of 15 J/m(2), CHO cells transfected with th e various hREC2/RAD51B vectors exhibited different responses. Cells ex pressing the wild-type human Rec2/Rad51B underwent apoptosis, with the greatest cell death occurring 24 h after irradiation. The control cel ls, which contained an empty vector, and the cells expressing truncate d hsRec2/Rad51B or the full-length Rec2 with a mutation at residue 163 did not. In summary, these findings of cell, cycle slowing and UV-ind uced apoptosis in CHO cells constitutively expressing the human Rec2/R ad51B protein suggest that hsRec2/Rad51B plays a role in a DNA damage surveillance pathway.