INDUCTION OF DNA SYNTHESIS IN CULTURED NEURONS BY ULTRAVIOLET LIGHT OR METHYL METHANE SULFONATE

Cellular DNA can suffer single-stranded chemical damage as a consequence of exposure to highenergy radiation or certain chemicals. Bacteria can repair this damage by excising a segment of the damaged strand and synthesizing a new segment complementary to the undamaged strand (14) . Mammalian cells can also be induced to synthesize small amounts of DNA, when they would not ordinarily be doing so, by exposing them to ultraviolet light (12), X rays (10), or certain alkylating agents (5, 13) . This "unscheduled DNA synthesis" has been demonstrated to be nonsemiconservative repair synthesis in a number of cases