Unscheduled DNA synthesis induced by 4-nitroquinoline-1-oxide in xeroderma pigmentosum cells and their complementing heterodikaryons.

Unscheduled DNA synthesis (UDS) induced by 4-nitroquinoline-1-oxide (rNQO) in the complementation groups A to E and variant xeroderma pigmentosum (XP) cells, and various pairs of complementing XP heterokaryons were investigated. The pattern of UDS induced by various concentrations of 4NQO in normal cells was quite different from those in groups A to D XP cells. The patterns of UDS in group E and variant XP cells were indistinguishable from those of normal cells under our experimental conditions. The levels of UDS induced by 5 x 10(-6) M 4NQO were 13% of normal in group A, 9% in group B, 17% in group C, 25% in group D. The heterokaryons obtained by pair-wise fusions between different complementation groups of XP strains showed restored UDS induced by 5 x 10(-6) M 4NQO, while the dikaryons obtained from fusion between the same groups did not.