Mutants of Escherichia coli unable to metabolize cytidine: Isolation and characterization
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Strains of Escherichia coli have been selected, which contain mutations in the udk gene, encoding uridine kinase. The gene has been located on the chromosome as cotransducible with the his gene and shown to be responsible for both uridine and cytidine kinase activities in the cell.
An additional mutation in the cdd gene (encoding cytidine deaminase) has been introduced, thus rendering the cells unable to metabolize cytidine. In these mutants exogenously added cytidine acts as inducer of nucleoside catabolizing enzymes indicating that cytidine per se is the actual inducer.
When the udk, cdd mutants are grown on minimal medium the enzyme levels are considerably higher than in wild type cells. Evidence is presented indicating that the high levels are due to intracellular accumulation of cytidine, which acts as endogenous inducer.
Abbreviations and Symbols
3, 4, 5, 6-tetrahydrouridine
deoxyuridine monophosphate. Genes coding for: cytidine deaminase
uridine kinase (=cytidine kinase)
- upp. CytR
regulatory gene for cdd, udp, dra, tpp, drm and pup
- EC 18.104.22.168
Purine nucleoside phosphorylase or purine nucleoside: orthophosphate (deoxy)-ribosyltransferase
- EC 22.214.171.124
thymidine phosphorylase or thymidine: orthophosphate deoxyribosyltransferase
- EC 126.96.36.199
uridine phosphorylase or uridine: orthophosphate ribosyltransferase
- EC 188.8.131.52
cytidine deaminase or (deoxy)cytidine aminohydrolase
- EC 184.108.40.206
deoxyriboaldolase or 2-deoxy-D-ribose-5-phosphate: acetaldehydelyase
- EC 220.127.116.11
UMP-pyrophosphorylase or UMP: pyrophosphate phosphoribosyltransferase
- EC 18.104.22.168
uridine kinase or ATP: uridine 5′-phosphotransferase
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