Abstract
Growth of E. coli 15 in the presence of 10 −4 m deoxythymidine 5′-monophosphate (dTMP) resulted in a 40% increase of the total thymine deoxynucleotide pool. In addition, there were (a) approximately 40% decreases of the uracil and cytosine deoxynucleotide pools, and of the contribution de novo to the thymine deoxynucleotide pool, (b) no significant changes in both the purine deoxynucleotide and pyrimidine ribonucleotide pools and (c) no change in ribonucleotide reductase activity. These results indicate that the decrease in pyrimidine deoxyribonucleotide biosynthesis is due to feedback inhibition rather than repression of ribonucleotide reductase. Greater than 65% inhibition of CDP reduction in vitro was observed when ATP, dATP, dGTP, dTTP, and dCTP were added at concentrations which approximated their normal intracellular concentrations. Alkaline phosphatase resistant nucleotides constituted a small percentage of the deoxynucleotide pools but as much as 46% of the ribonucleotide pools. The measureable uracil deoxynucleotide pool was composed entirely of alkaline phosphatase resistant nucleotides.
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