Primary site of reaction in the in vitro complex of phleomycin in DNA

Single-strand and double-strand deoxyribonucleic acid breaks produced by several bleomycin analogues

Production of single-strand breaks (ssb) and double-strand breaks (dsb) of PM2 phage DNA by several structurally related bleomycin (BLM) analogues was studied by gel electrophoresis. BLM A2 and BLM B2 produced a comparable extent of dsb. In various experiments, BLM A2 and BLM B2, at 22-41 ng/mL, degraded 50% of the form I DNA into 33-38% form II and 12-17% form III DNA. BLM B1' produced ssb and dsb at a ratio similar to that of BLM A2, but both at a rate less than half that of BLM A2. Phleomycin (PLM) D1 induced an equivalent amount of ssb but only one-eighth of dsb induced by BLM B2. The relatively lower extent dsb production for PLM D1 was observed either in borate buffer (pH 9.5) or in Tris-HCl buffer (pH 7.5) and in the presence or absence of exogenous Fe(II). Deamido-BLM A2 produced ssb to an extent approximately half that of BLM A2 and dsb to less than one-eighth that of BLM A2. The following conclusions were drawn. (1) BLM analogues produced ssb and dsb to different extents and ratios. (2) The ratio of dsb to ssb varied depending on the analogue, indicating a lack of a direct correlation between ssb and dsb. (3) The extent of ssb and dsb was affected by modifications on both the C- and N-terminal half-molecules of BLM: modification of either the N-terminal amide or the bithiazole greatly reduced dsb, whereas changes in structure or charge in the C-terminal amine affected ssb and dsb to a similar extent.

Phileomycin-induced lethality and DNA degradation in Escherichia coli K12

The cell lethality and DNA fragmentation caused by phleomycin (PM) were studied in E. coli K12 strains with special reference to the effects of repair or recombination deficiences and metabolic inhibitors. (1) Unlike excision-defective derivatives of E. coli B, uvrA, uvrB, and uvrC mutants of strain K12 showed no peculiarities compared with wild type in regard to cell survival. Likewise, mutant alleles at uvrD and polA loci had no effect. In contrast, rec mutants were more sensitive to PM-killing than were rec+ strains. (2) PM-induced strand breakage in DNA was observed in all strains tested including the above-mentioned mutants. There was no significant distinction between the uvr mutants and the wild type strain, indicating that the uvr-endonuclease was not responsible for the strand breaks. Involvement of endonuclease I was also ruled out. (3) At least some of the PM-induced breaks were repairable. (4) PM-induced lethality and strand breakage were totally dependent on energy supply. Inhibition of protein synthesis resulted in a partial and parallel suppression of the two effects. Our results suggest that the lethality is due to DNA strand breakage and the repair of such damage is postulated to be controlled by rec genes.

Anti-mitotic activity of bleomycin: time of action in the mammalian cell cycle

Bleomycin inhibits cell division in HeLa S-3 and other mammalian epithelial cell lines. Its effect on suspension cultured cells is far greater than on monolayer cells; this was found to be due partly to the absence of divalent ions. Other mammalian epithelial lines in suspension culture are very sensitive but fibroblastic cells (BHK 21/C13/DWS-3) grown under identical conditions are relatively insensitive. This study has established that bleomycin is a powerful anti-mitotic agent during the G(2) phase but it does not prevent prophase cells from completing a normal mitotic division. Its ability to suppress DNA synthesis contributes little to the inhibition of cell cycling.

Phleomycin-stimulated degradation of deoxyribonucleic acid in Escherichia coli

Phleomycin stimulates the degradation of DNA by energy-dependent endonuclease and exonuclease reactions in Escherichia coli rec(+) cells and in recB(-) and recC(-) cells that lack an adenosine triphosphate-dependent nuclease functioning in the repair of ultraviolet (UV) lesions. Exonuclease activity is blocked in T4 phage-infected cells. The endonuclease reaction produces 10(7)-dalton segments resembling those produced in colicin E2-treated cells. These differ from the random-sized segments produced in UV-irradiated cells, or the 10(6)-dalton segments made in T4 phage-infected cells. A mutant selected for phleomycin tolerance is cross-tolerant to colicin E2, and some mutants selected for colicin E2 tolerance are cross-tolerant to phleomycin. On the basis of these cross-tolerances and the similarities between the effects of phleomycin and E2-stimulated nucleases, the suggestion is made that both agents may stimulate the same nuclease reactions in E. coli cells.