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Summary: Treatment of growing Mycobacterium smegmatis with hydroxyurea decreased the DNA/protein ratio and markedly increased the specific activities of DNA polymerase and ATP-dependent deoxyribonuclease. These changes were similar to those produced by iron limitation of growth. Treating M. smegmatis with nalidixic acid also decreased the DNA/protein ratio but had no effect on the activity of either enzyme. Growth of M. smegmatis under conditions of zinc limitation did not diminish the specific activity of DNA polymerase thus not favouring a role for zinc in the action of this enzyme. The activity of the ATP-dependent deoxyribonuclease was, however, slightly increased. In previous reports the specific activity of DNA polymerase in this organism has been seriously underestimated due to interfering deoxyribonuclease and nucleoside triphosphatase. This was corrected by sufficient dilution of the extract. Revised specific activities of DNA polymerase in carbon-limited, nitrogen-limited and iron-limited cultures are, respectively, 10, 14, 11 and 64 units/mg protein.

Effects of Hydroxyurea, Nalidixic Acid and Zinc Limitation on DNA Polymerase and ATP-dependent Deoxyribonuclease Activities of Mycobacterium smegmatis