Abstract
Using a genetic screen we have identified two chromosomal genes,
cusRS
(
ylcA ybcZ
), from
Escherichia coli
K-12 that encode a two-component, signal transduction system that is responsive to copper ions. This regulatory system is required for copper-induced expression of
pcoE
, a plasmid-borne gene from the
E. coli
copper resistance operon
pco
. The closest homologs of CusR and CusS are plasmid-borne two-component systems that are also involved in metal responsive gene regulation: PcoR and PcoS from the
pco
operon of
E. coli
; CopR and CopS from the
cop
operon, which provides copper resistance to
Pseudomonas syringae
; and SilR and SilS from the
sil
locus, which provides silver ion resistance to
Salmonella enterica
serovar Typhimurium. The genes
cusRS
are also required for the copper-dependent expression of at least one chromosomal gene, designated
cusC
(
ylcB
), which is allelic to the recently identified virulence gene
ibeB
in
E. coli
K1. The
cus
locus may comprise a copper ion efflux system, because the expression of
cusC
is induced by high concentrations of copper ions. Furthermore, the translation products of
cusC
and additional downstream genes are homologous to known metal ion antiporters.
