Molecular and General Genetics MGG

, Volume 126, Issue 2, pp 177-186

First online:

Mutants of Escherichia coli unable to metabolize cytidine: Isolation and characterization

  • Karin Hammer-JespersenAffiliated withInstitute of Biological Chemistry B, University of Copenhagen
  • , Agnete Munch-PetersenAffiliated withInstitute of Biological Chemistry B, University of Copenhagen

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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.