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Increased DNA polymerase and ATP-dependent deoxyribonuclease activities following DNA damages in mycobacterium
Abstract:
Treatment of growing cultures of Mycobacterium smegmatis with alkylating agents (methyl methanesulphonate, ethyl methanesulphonate, nitrogen mustard, or mitomycin C) or with ultraviolet light resulted in enhanced specific activities of a DNA polymerase and of an ATP-dependent deoxyribonuclease. Similar results had previously been obtained with hydroxyurea and with iron limitation. The three of these treatments which were tested (methyl methanesulphonate, mitomycin C and hydroxyurea) produced strand breaks or alkali-labile regions in the DNA of this organism. The increased enzyme activities could be prevented by simultaneous treatment with inhibitors of protein synthesis. In contrast, treatment of the cultures with intercalating agents (ethidium bromide, acridine orange, or proflavine), 5-fluorouracil, caffeine, or nalidixic acid, inhibited DNA synthesis without increasing the enzyme activities. These treatments did not produce strand breaks in the DNA of this organism. The results support the hypothesis that, in M. smegmatis, damage to DNA induces increased synthesis of enzymes associated with DNA repair.
Insights
DNA damage in Mycobacterium smegmatis, caused by agents like methyl methanesulphonate or UV light, enhances DNA repair enzyme activity. This response is blocked by inhibiting protein synthesis.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- DNA repair mechanisms are crucial for microbial survival.
- Understanding how DNA damage affects enzyme synthesis in Mycobacterium smegmatis is important.
Purpose of the Study:
- To investigate the effect of DNA-damaging agents on DNA repair enzyme activity in Mycobacterium smegmatis.
- To determine if DNA damage induces the synthesis of DNA repair enzymes.
Main Methods:
- Exposing Mycobacterium smegmatis cultures to various DNA-damaging agents (alkylating agents, UV light) and non-damaging agents.
- Measuring the specific activities of DNA polymerase and ATP-dependent deoxyribonuclease.
- Assessing DNA integrity by detecting strand breaks or alkali-labile regions.
- Investigating the role of protein synthesis using inhibitors.
Main Results:
- Alkylating agents and UV light significantly increased DNA polymerase and deoxyribonuclease activity.
- DNA-damaging treatments induced DNA strand breaks or alkali-labile regions.
- Inhibitors of protein synthesis prevented the increase in enzyme activity.
- Intercalating agents and other tested compounds inhibited DNA synthesis but did not increase enzyme activity and did not cause DNA strand breaks.
Conclusions:
- DNA damage in Mycobacterium smegmatis triggers an increase in the synthesis of DNA repair enzymes.
- The observed increase in enzyme activity is dependent on concurrent protein synthesis.
- These findings support a model where DNA damage directly induces DNA repair pathways.