Sj. Beard et al., ZINC(II) TOLERANCE IN ESCHERICHIA-COLI K-12 - EVIDENCE THAT THE ZNTA GENE (O732) ENCODES A CATION-TRANSPORT ATPASE, Molecular microbiology, 25(5), 1997, pp. 883-891
A transposon (Tn 10dCam) insertion mutant of Escherichia coli K-12 was
isolated that exhibited hypersensitivity to zinc(II) and cadmium(II)
and, to a lesser extent, cobalt(II) and nickel (II). The mutated gene,
located between 75.5 and 76.2 min on the chromosome, is named zntA (f
or Zn(II) transport or tolerance). The metal-sensitive phenotype was c
omplemented by a genomic DNA clone mapping at 3677.90-3684.60 kb on th
e physical map. Insertion of a kanamycin resistance (Kn(R)) cassette a
t a SalI site in a subcloned fragment generated a plasmid that partial
ly complemented the zinc(II)-sensitive phenotype. DNA sequence analysi
s revealed that the Kn(R) cassette was located within the putative pro
moter region of an ORF (o732 or yhhO) predicted to encode a protein of
732 amino acids, similar to cation transport P-type ATPases in the Cp
x-type family. Inverse PCR and sequence analysis revealed that the Tn1
0dCam element was located within o732 in the genome of the zinc(II)-se
nsitive mutant. The zntA mutant had elevated amounts of intracellular
and cell surface-bound Zn(II), consistent with the view that zntA(+) e
ncodes a zinc(II) efflux protein. Exposure of the zntA mutant to cobal
t(II) and cadmium(II) also resulted in elevated levels of intracellula
r and cell surface-bound metal ions.