[Absence of interstrand cross-links in DNA treated wtih 3-carbethoxypsoralen and 365 nm irradiation]

In contrast to 8-MOP photoaddition on DNA, the renaturation capacity of heat or alkali denatured DNA treated with 3-CPs is absent. This shows that DNA interstrand cross-links are not produced by 3-CPs photoaddition even by a dose which leads to 10(-5) survivors. At equimolar concentrations of 3-CPs or 8-MOP (5 x 10(-4) M) and a dose of 10 kJ.m-2 of 365 nm radiation, 1 molecule of 3-CPs for 4 x 10(3) nucleotides and 1 molecules of 8-MOP for 9 x 10(3) nucleotides are fixed in vivo. Since wild type cells are about 4 times more sensitive to 8-MOP than to 3-CPs photoaddition, it implies that cross-links are important in genotoxicity and that monoadditions are more easily repaired than cross-links.