Cloning and expression of R-factor mediated arsenate resistance in Escherichia coli.

The resistance transfer factor R773 confers inducible arsenate, arsenite and antimony resistance on Escherichia coli. The genes for these resistances were cloned into the EcoRI site of plasmid pBR322 to produce a 33 kilobase plasmid. pUM1. Bacterial strains transformed with pUM1 synthesized a polypeptide of the apparent molecular weight 64,000 daltons when induced with arsenite. This polypeptide could be visualized on sodium dodecyl sulfate polyacrylamide gels stained with Coomassie blue. It was observed both in the membrane and cytosol fractions but not among the periplasmic proteins present in osmotic shock fluid. Minicells isolated from strain JR410(pUM1) incorporated [35S]methionine into an inducible 64,000 dalton polypeptide, as demonstrated on autoradiographs of electrophoresed [35S]-labeled minicell lysates, confirming that this polypeptide is a plasmid gene product. A 4.3 kilobase HindIII fragment of pUM1 was subcloned into the HindIII site of pBR322, producing recombinant plasmid pUM3. This plasmid conferred constitutive resistance ot arsenite and arsenate. Extensive synthesis of two polypeptides of 64,000 and 16,000 daltons was observed both in Coomassie stained gels of whole cells and autoradiographs of gels of [35S]methionine-labeled minicells. Synthesis of both polypeptides was constitutive.