Characterization of the Escherichia coli codBA operon encoding cytosine permease and cytosine deaminase.
The nucleotide sequence of a 3.1 kb segment carrying the cytosine deaminase gene (codA) from Escherichia coli was determined. The sequence revealed the presence of two open reading frames, the first (codB) specifying a highly hydrophobic polypeptide and the second specifying cytosine deaminase. A two-codon overlap between the two reading frames indicates that they constitute an operon. Transcription of the operon was found to be regulated by exogenous purines. Polypeptides specified by each of the two reading frames were expressed in minicells, and the codB gene product was found to be highly enriched in the membrane fraction. Uptake experiments showed that the CodB protein is required for cytosine transport into the cell and that the intracellular accumulation of cytosine correlated with the codB gene dose. A topological model for the cytosine permease in the cytoplasmic membrane is proposed.
Danielsen
S
S
Institute of Biological Chemistry B, University of Copenhagen, Denmark.
Kilstrup
M
M
Barilla
K
K
Jochimsen
B
B
Neuhard
J
J
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D003596:Cytosine / Q000378:metabolism*; D043525:Cytosine Deaminase; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D005798:Genes, Bacterial; D026901:Membrane Transport Proteins / Q000235:genetics*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009700:Nucleoside Deaminases / Q000235:genetics* / Q000378:metabolism; D016366:Open Reading Frames; D009876:Operon; D011687:Purines / Q000494:pharmacology
D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D011687:Purines; C075818:codB protein, E coli; D003596:Cytosine; D009700:Nucleoside Deaminases; D043525:Cytosine Deaminase; C468827:codA protein, E coli