Mercuric ion uptake by Escherichia coli cells producing Thiobacillus ferrooxidans merC

The merC gene of Thiobacillus ferrooxidans was overexpressed in Escherichia coli under the control of the tac promoter. MerC protein synthesized in E. coli has a N-terminal amino acid sequence of S-A-I-X-R-I-I-D-K-I-G-I-V-G-, which agrees with the amino acid sequence deduced from its nucleotide sequence except that an initiating methionine residue was removed. The MerC protein was localized in the particulate (membrane) cell fraction, and not in the soluble cytoplasmic fraction. E. coli cells carrying a plasmid containing the tac promoter-directed merC showed 203Hg2+ uptake in an isopropyl-1-thio-beta-D-galactopyranoside (IPTG)-dependent manner.