Scissions of proteins linking DNA in cultured mammalian cells induced by 4-nitroquinoline 1-oxide and their repair.

of breakage increased, recovery was incomplete, and the fraction which was still unrepaired after recovery incubation increased. Concomitant with repair of DNA the growth capacity of the cells was regained. However, as the unrepaired fraction increased with increase in the concentration of 4NQO, the viability of the cells decreased. Cell killing induced by 4NQO was suggested to be due to disorder of cell functions caused by irreparable double-strand scission of DNA. With a sucrose gradient containing Pronase, it was found that treatment of the cells with the lower concentrations of 4NQO, i.e., 1 X 10"s M for L-P3 cells and 1 X IO'6 M for