Abstract: Metallothioneins （MTs） are low molecular weight, metal-binding and cysteine rich proteins found in a variety of living organisms. In this study, a 408 bp cDNA encoding for a metallothionein was cloned from housefly （Musca domestica） by RACE based on EST information and named as MdMtn （GenBank accession no. GU289398）. Sequence analysis showed that MdMtn contains a 123 bp open reading frame （ORF） encoding a protein of 40 amino acid residues. The MdMtn peptide sequence includes 10 cysteine residues with a distribution pattern of -C-X-C-.The predicted molecular weight of encoding protein is 3.8 kD with the isoelectric point （pI） of 8.78. In order to detect the MdMtn activity in binding heavy metals, the target gene was cloned into a prokaryotic expression vector pET-DsbA, and then a fusion protein was expressed in Escherichia coli BL21（DE3）. It was found that in the presence of CdCl2, the expression of MdMtn significantly increased the bacteria tolerance to Cd²⁺, suggesting that MdMtn may play an active role in housefly adaption to the environment with heavy metals.

Key words: Musca domestica, metallothionein, gene cloning, prokaryotic expression, protein activity