Nivalenol, a toxic product isolated from the rice grains infected with Fusarium nivale, was shown to inhibit the multiplication of HeLa cells completely at a concentration of 0.5μg/ml or higher. At the concentration of 5μg/ml, protein and DNA syntheses were almost entirely suppressed, whereas little or no inhibition took place in RNA synthesis. The inhibitory effects on both DNA and protein syntheses were similar with respect to the rapidity and severity.
Cell cycle analysis revealed that, in addition to direct effect on S phase, the toxin affected the entry of G1 cells into S phase and that of G2 cells into mitosis. These results are discussed with special reference to the similarity of the action to that of well-known inhibitors for protein synthesis.