REPRESSION BY ADENINE OF THE FORMYLTETRAHYDROFOLATE SYNTHETASE IN AN ANTIFOLIC-RESISTANT MUTANT OF STREPTOCOCCUS FAECALIS.

Albrecht, Alberta M. (Sloan-Kettering Institute for Cancer Research, New York, N.Y.), and Dorris J. Hutchison. Repression by adenine of the formyltetrahydrofolate synthetase in an antifolic-resistant mutant of Streptococcus faecalis. J. Bacteriol. 87:792-798. 1964.-In an amethopterin-resistant mutant of Streptococcus faecalis ATCC 8043 under cultivation conditions requiring purine synthesis de novo, both the dihydrofolate reductase and the formyltetrahydrofolate synthetase were formed as constant fractions of the total protein synthesized during the exponential phase of growth. When excess adenine was added to the medium, the rate of formation of the synthetase was markedly decreased, i.e., repressed. Under these latter conditions, the synthesis of the reductase proceeded at a rate equal to that observed in the absence of adenine. The repressibility of the synthetase by adenine was demonstrated also by the decrease in rate of synthetase formation upon the addition of adenine to a culture actively synthesizing this enzyme. Guanine and hypoxanthine, like adenine, also repressed the synthetase; exogenous xanthine was less effective. Neither of the pyrimidines, thymine and uracil, at approximately 1 mug/ml, interfered with synthesis of the two enzymes.