1.A.72.4.2
Mercuric transport channel protein, MerC, of 144 aas and 4 TMSs.  Cys-23 and Cys-26 of the protein were involved in Hg²⁺-recognition/uptake, but Cys-132 and Cys-137 were not (Sasaki et al. 2005). E. coli cells producing MerC were hypersensitive to CdCl₂. In this case, mutation of His72 rendered the host cells less CdCl₂ sensitive, whereas none of the Cys residues affected it. E. coli cells expressing a merC-deletion mutant, in which the coding-sequence of the carboxy-terminal cytoplasmic region was removed, retained Hg²⁺ hypersensitivity and showed about 55% HgCl₂ uptake ability compared to that of the one expressing the intact merC, indicating that this region is not essential for Hg²⁺ uptake. Coexpression of the A. ferrooxidans gene encoding mercuric reductase (merA) and the merC deletion mutation conferred HgCl₂ tolerance to E. coli host cells. Under this condition, the merC deletion gene product was exclusively present as a monomer (Sasaki et al. 2005).