Phileomycin-induced lethality and DNA degradation in Escherichia coli K12

Responses of radiation-sensitive mutants of Saccharomyces cerevisiae to lethal effects of bleomycin

Haploid and diploid strains of yeast containing genes conferring radiation-sensitivity were studied under growing and nongrowing experimental conditions for their relative sensitivities to growth-inhibitory effects of bleomycin (BM). The rad1, rad2, rad3, rad4, rad5 (and allelic rev2), rad7, rad10, rad11, rad 12, rad14, rad15, rad16 and rev3 strains exhibited responses similar to normal (Rad+) yeast strains. It is concluded from these findings that the excision-repair function deficient in several of these mutant strains is not important for repair of bleomycin-induced damages in yeast. The sensitive strains contained rad6, rad9, rad18, rad22, rad50, rad51, rad52, rad53, rad54, rad55, rad56, rad57 and rs1. Strains bearing rad8 or rad19 could not be classified unambiguously. With one exception, all rad mutants found very sensitive to BM were sensitive to X-rays, suggesting that some aspect of the repair of BM- and X-ray-induced damages in yeast may be similar. Sensitivities to BM and radiation co-segregated in pedigrees following meiosis, and several BM-resistant revertants isolated from two rad6 mutant strains sensitive to BM, X-rays and UV were cross-resistant to all three agents. These results confirm that the rad mutants were responsible for the cross-sensitivities in the original strains.

CIBA 36278-Ba" chemotherapy and toxicology in laboratory animals

Phleomycin (PM) induces rapid solubilization of deoxyribonucleic acid (DNA), inhibition of cellular mass increase, and loss of viability when added either to growing cultures of Escherichia coli B or an endonuclease I-defective derivative of B. Nonetheless, bacteriophage of the T-even series are produced, albeit to a reduced extent, when PM is added with phage or after infection to E. coli cells. Bacteriophage T4 infection inhibits the ability of PM to bring about the solubilization of DNA; this effect appears to account for most of the resistance of T-even phage replication to PM. The patterns of inhibition of phage yields obtained when PM is added at infection suggest that glucosylation of T-even phage DNA may also have a protective effect. However, PM induces the solubilization of glucosylated and nonglucosylated DNA at approximately the same rate and thermal denaturation studies indicate that the antibiotic binds both types of DNA equally well. The latter experiments also provided evidence that PM dissociates from DNA at temperatures greater than 80 C.

The mechanism of DNA breakage by phleomycin in vitro

Phleomycin induces DNA breakage in vitro in the presence of the sulphydryl compound dithiothreitol. The reaction appears to be free radical-mediated, and requires oxygen and metal ions. Reaction rate is limited by the concentration of oxygen, which is converted to hydrogen peroxide during DNA breakage. However there is no net change in the sulphydryl compound. The proposed reaction mechanism involves metal ion/oxygen-catalysed oxidation of dithiothreitol to its free radical form, which reacts with phleomycin, leading to formation of activated phleomycin and regeneration of free sulphydryl. Free phleomycin is converted to an inactive form, but activation of phleomycin bound to DNA leads to DNA breakage.