De novo synthesis of thymidylate via deoxycytidine in dcd (dCTP deaminase) mutants of Escherichia coli

J Bacteriol. 1994 Apr;176(8):2194-9. doi: 10.1128/jb.176.8.2194-2199.1994.


dcd (dCTP deaminase) mutants of Escherichia coli were reported not to require thymidine for growth even though most of the thymidylate that is synthesized de novo arises from cytosine nucleotides through a pathway involving dCTP deaminase. We found, however, that the fresh introduction of dcd mutations into many strains of E. coli produced a requirement for thymidine for optimum aerobic growth, but the mutants readily reverted to prototrophy via mutations in other genes. One such mutation was in deoA, the gene for deoxyuridine phosphorylase. However, a dcd deo mutant became thymidine dependent once again if a cdd mutation (affecting deoxycytidine deaminase) were introduced. The results indicate that dcd mutants utilize an alternative pathway of TMP synthesis in which deoxycytidine and deoxyuridine are intermediates. A cdd mutation blocks the pathway by preventing the conversion of deoxycytidine to deoxyuridine, whereas a deoA mutation enhances it by sparing deoxyuridine from catabolism. The deoxycytidine must arise from dCTP or dCDP via unknown steps. It is not known to what extent this pathway is utilized in wild-type cells, which, unlike the dcd mutants, do not accumulate dCTP.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anaerobiosis
  • Bromodeoxyuridine / pharmacology
  • Deoxycytidine / genetics
  • Deoxycytidine / metabolism*
  • Escherichia coli / drug effects
  • Escherichia coli / genetics
  • Escherichia coli / growth & development
  • Escherichia coli / metabolism*
  • Genes, Bacterial / genetics
  • Genes, Bacterial / physiology*
  • Genetic Complementation Test
  • Mutation / genetics
  • Mutation / physiology
  • Nucleotide Deaminases / genetics
  • Nucleotide Deaminases / metabolism*
  • Pentosyltransferases / genetics
  • Pyrimidines / metabolism
  • Thymidine Monophosphate / biosynthesis*
  • Thymidine Phosphorylase / metabolism
  • Uridine Phosphorylase


  • Pyrimidines
  • Deoxycytidine
  • Thymidine Monophosphate
  • Pentosyltransferases
  • Uridine Phosphorylase
  • deoxyuridine phosphorylase
  • Thymidine Phosphorylase
  • Nucleotide Deaminases
  • dCTP deaminase
  • Bromodeoxyuridine