Aflatoxin B1, a selective inhibitor of DNA synthesis in mammalian cells

Aflatoxin B1 in concentrations between 0.01 and 0.1 microgram/ml inhibits DNA synthesis in African green monkey cells in culture, but has little effect on RNA synthesis and no effect on protein synthesis. The drug even at concentrations up to 1.0 microgram/ml does not interfere with DNA repair promoted by ultraviolet irradiation nor does it induce DNA repair. The inhibition of DNA synthesis attains maximum values 3 h after addition of aflatoxin B1 and is irreversible upon removal of the drug. Profiles of pulselabeled DNA sedimented in alkaline sucrose gradients indicate that aflatoxin B1 blocks initiation of replication rather than elongation.