Sequence analysis and expression of the bacterial dichloromethane dehalogenase structural gene, a member of the glutathione S-transferase supergene family

Abstract

The nucleotide sequence of a cloned 2.8-kilobase-pair BamHI-PstI fragment containing dcmA, the dichloromethane dehalogenase structural gene from Methylobacterium sp. strain DM4, was determined. An open reading frame with a coding capacity of 287 amino acids (molecular weight, 37,430) was identified as dcmA by its agreement with the N-terminal amino acid sequence, the total amino acid composition, and the subunit size of the purified enzyme. Alignment of the deduced dichloromethane dehalogenase amino acid sequence with amino acid sequences of the functionally related eucaryotic glutathione S-transferases revealed three regions containing highly conserved amino acid residues and indicated that dcmA is a member of the glutathione S-transferase supergene family. The 5' terminus of in vivo dcmA transcripts was determined by nuclease S1 mapping to be 82 base pairs upstream of the GTG initiation codon of dcmA. Despite a putative promoter sequence with high resemblance to the Escherichia coli -10 and -35 consensus sequences, located at an appropriate distance from the transcription start point, dcmA was only marginally expressed in E. coli. The strong induction of dichloromethane dehalogenase in Methylobacterium sp. by dichloromethane was abolished by deleting the 1.3-kilobase-pair upstream region of dcmA. Plasmid constructs devoid of this region directed expression of dichloromethane dehalogenase at a constitutively induced level.