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Lethal effect of mitomycin C on Haemophilus influenzae
Abstract:
The sensitivity of ultraviolet-sensitive strains to inactivation by mitomycin C (MC) is at the most only a factor of two greater than that of the wild type. The presence of inducible prophage has very little effect on the sensitivity. Genes which control excision of ultraviolet-induced pyrimidine dimers also control repair of MC-induced cross-links, as measured by resistance of denatured deoxyribonucleic acid (DNA) from treated cells to S1 nuclease digestion. However, endonucleolytic breaks in MC-damaged DNA, as judged by decreased single-strand molecular weight upon incubation of treated cells, are independent of these genes and probably are caused by monoadducts. After long periods of incubation there is a return to the molecular weight of untreated DNA. DNA degradation after MC treatment of various strains is not correlated with sensitivity to inactivation. Stationary-phase cells of all strains are more than twice as sensitive to MC as exponentially growing cells, and the sensitivity difference agrees with the measured difference in the number of cross-links after MC treatment of cells in the two growth stages. Evidence has been obtained that these phenomena result from differences in uptake of MC, which can be influenced by cyclic adenosine monophosphate. Small deviations in MC sensitivity from that of the wild type observed in mutants lacking the adenosine 5'-triphosphate-dependent nuclease are postulated to result from differences in MC uptake. These mutants, although no more ultraviolet sensitive than the wild type, are more sensitive to streptomycin, which also must be taken up by the cell to be effective.
Insights
Mitomycin C (MC) inactivation sensitivity is linked to DNA repair genes and cell growth phase. Stationary cells show higher sensitivity due to differences in MC uptake, influenced by cyclic adenosine monophosphate.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Mitomycin C (MC) is a chemotherapeutic agent that induces DNA cross-links.
- Understanding DNA repair mechanisms is crucial for cancer treatment and drug resistance.
- The role of specific genes and cellular conditions in MC sensitivity requires further elucidation.
Purpose of the Study:
- To investigate the relationship between DNA repair genes and sensitivity to mitomycin C (MC).
- To explore the impact of cell growth phase and prophage presence on MC inactivation.
- To determine the mechanisms underlying differential MC sensitivity in various bacterial strains.
Main Methods:
- Assessing sensitivity of ultraviolet-sensitive strains and wild-type strains to MC.
- Measuring DNA integrity using S1 nuclease digestion after MC treatment.
- Analyzing DNA single-strand molecular weight changes upon cell incubation.
- Comparing MC sensitivity between stationary and exponentially growing cells.
Main Results:
- Genes controlling pyrimidine dimer excision also govern MC cross-link repair, but not endonucleolytic breaks.
- Stationary-phase cells are significantly more sensitive to MC than exponentially growing cells, correlating with cross-link formation.
- Differences in MC uptake, potentially mediated by cyclic adenosine monophosphate, influence sensitivity.
- Mutants lacking adenosine 5'-triphosphate-dependent nuclease show altered MC sensitivity due to uptake variations.
Conclusions:
- DNA repair genes play a role in repairing MC-induced cross-links, but not monoadduct-induced breaks.
- Cellular uptake of MC is a critical factor determining sensitivity, particularly between different growth phases.
- Cyclic adenosine monophosphate may regulate MC uptake and subsequent cellular response.
- Further research into MC uptake mechanisms can inform therapeutic strategies.