The Listeria monocytogenes gene ctpA encodes a putative P-type ATPase involved in copper transport

A Tn917 transposon derivative was used to construct a lacZ transcriptional fusion mutant in Listeria monocytogenes DRDC8 that displayed increased β-galactosidase activity in response to cation stress. A 4.3 kb fragment of L. monocytogenes chromosomal DNA flanking the lacZ fusion was cloned and sequenced. A 1962 bp open reading frame was identified, and designated ctpA. Analysis of the deduced 653 amino acid sequence revealed significant similarity to the family of ATP-dependent enzymes involved in copper transport in prokaryotes and eukaryotes. CtpA is distinctive by virtue of an N-terminal truncation in the domain responsible for cation binding. Growth of ctpA insertion mutants was restricted by the copper-chelating agent 8-hydroxyquinoline. DNA/RNA hybridisation studies revealed that levels of ctpA mRNA were increased following growth in media containing low and high copper concentrations. These results suggest the isolation of a region of DNA that encodes a novel copper-transporting system in L. monocytogenes.