The MerE protein encoded by transposon Tn21 is a broad mercury transporter in Escherichia coli

In order to clarify the physiological role of the merE gene of transposon Tn21, a pE4 plasmid that contained the merR gene of plasmid pMR26 from Pseudomonas strain K-62, and the merE gene of Tn21 from the Shigella flexneri plasmid NR1 (R100) was constructed. Bacteria with plasmid pE4 (merR-o/p-merE) were more hypersensitive to CH3Hg(I) and Hg(II), and took up significantly more CH3Hg(I) and Hg(II), than the isogenic strain. The MerE protein encoded by pE4 was localized in the membrane cell fraction, but not in the soluble fraction. Based on these experimental results, we suggest for the first time that the merE gene is a broad mercury transporter mediating the transport of both CH3Hg(I) and Hg(II) across the bacterial membrane.