Plasmid pAO1 of Arthrobacter oxidans encodes 6-hydroxy-D-nicotine oxidase: cloning and expression of the gene in Escherichia coli.

The 160 kb plasmid pAO1 from Arthrobacter oxidans (Brandsch and Decker 1984) was subcloned in Escherichia coli with the aid of the plasmid vectors pUR222 and pBR322. Screening of the recombinant clones for enzyme activity revealed that the flavoenzyme 6-hydroxy-D-nicotine oxidase (6-HDNO), one of the enzymes of the nicotine-degradative pathway in A. oxidans, is encoded on pAO1. Immunoprecipitation of 35S-methionine-labelled E. coli cells with 6-HDNO-specific antiserum and expression of recombinant plasmid DNA in E. coli "maxicells" revealed that 6-HDNO is made as a 52,000 dalton protein, approximately 4,500 daltons larger than 6-HDNO from A. oxidans. The 6-HDNO activity was constitutively expressed in E. coli cells, possibly from an A. oxidans promoter, as shown by subcloning of the 6-HDNO gene in pBR322, using the expression vector pKK223-3 and the promoter probe vector pCB192.