The role of cysteine residues in the transport of mercuric ions by the Tn501 MerT and MerP mercury‐resistance proteins

Abstract

Each cysteine residue in the MerT and MerP polypeptides of bacterial transposon Tn501 was replaced by serine, and the mercury-resistance phenotypes of the mutants were determined in Escherichia coli. Cys-24 and Cys-25 in the first transmembrane region of MerT were essential for transport of mercuric ions through the cytoplasmic membrane, and mutations Cys-76-Ser, Cys-82-Ser or Gly-38-Asp in MerT or Cys-36-Ser in MerP all reduced transport and resistance. Deletion of the merP gene slightly reduced mercuric ion resistance and transport, whereas a Cys-33-Ser mutation in MerP appears to block transport of mercuric ions by MerT. The effects of deleting merP on mutations in merT were tested. The 116-amino-acid MerT protein is sufficient for mercuric ion transport across the cytoplasmic membrane.