The lethal actions of mitomycin C and actinomycin D were followed during the division cycle of HeLa cells. The cells were most susceptible to a 2 hr pulse of mitomycin C during the G1 phase, whereas their sensitivity to actinomycin D was most pronounced in the S phase. Posttreatment of the cells with acetoxycycloheximide, a potent inhibitor of protein synthesis, increased the survival (colony-f...

SUMS{ARY The fine structure of stock IIeLa cells has been examined, and several new details have been described. Certain specific structural alterations induced by actinomycin D, a cytotoxic antibiotic, have been noted. These alterations included cytoplasmic blebbing and a fragmentation of the nucleoli accompanied by a pronounced loss in their osmiophilia, tteLa cells made resistant to actinomy...

Using actinomycin-producing and nonproducing strains of Streptomyces antibioticus, I studied several steps in the biosynthetic pathway of this antibiotic. Actinomycin-nonproducing strains derived after acriflavine or novobiocin treatment showed activity of kynurenine formamidase and phenoxazinone synthase as high as that of the parental strain, but these nonproducing strains failed to convert 4...

At high concentrations (10 mug/ml), actinomycin D inhibited deoxyribonucleic acid (DNA) synthesis in Bacillus subtilis. Inhibition occurred quickly (in less than 1 min) and was complete. In strain 23 thy his, inhibition of DNA synthesis by actinomycin D was followed by partial degradation of one of the two daughter strands to acid-soluble products. Degradation began at the replication point and...

BACKGROUND Gestational trophoblastic neoplasia (GTN) refers to malignant lesions that arise from abnormal proliferation of placental trophoblast. Even in its metastatic forms GTN is curable with a cure rate of 90-100 %. Currently, methotrexate with or without folic acid, andactinomycin D is recommended for low risk GTN. The aim of this study is to compare the efficacy of methotrexate and actino...

A subline of the L5178Y murine leukemia was selected for resistance to actinomycin D by drug administration in vivo. The resistant Une, L5178Y/D, had impaired capacity for uptake of actinomycin D in vivo and in culture but not under nongrowing conditions. Administration of the drug in vivo (50 jug/kg) or in culture (0.1 jug/ml) inhibited uridine incorporation into RNA by L5178Y but not by L5178...