Enhancement of Ultraviolet or N‐methyl‐n'‐ Nitro‐n‐nitrosoguanidine Sensitivity of Dictyostelium Discoideum by 3‐aminobenzamide

The amoeboid cells of Dktyostelium discoideumNC–4 possess a 3‐aminobenzamide(3‐ABA)‐sensitive repair mechanism for DNA damages induced by UV‐irradiation or N‐methyl‐N'‐nitro‐N‐nitrosoguanidine (MNNG)‐treatment. We have studied the effect of 3‐ABA on each step of excision repair in the UV‐ irradiated cells. Although the nicking of DNA‐strand and the excision of pyrimidine dimcrs are insensitive to 3‐ABA, the rejoining of DNA strand‐breaks is sensitive. The frequency of mutation induced by UV‐irradiation or MNNG‐treatment is depressed by 3‐ABA. The mechanisms of repair inhibition by 3‐ABA are discussed.