The purB gene of Escherichia coli K-12 is located in an operon

Department of Biochemistry, University of Southampton, Biomedical Sciences Building, Bassett Crescent East, Southampton SO16 7PX, UK ABSTRACT The structural gene ( purB ) for succinyl-AMP (S-AMP) lyase and three additional ORFs are on the same DNA strand of the chromosome of Escherichia coli. Cassette mutagenesis and primer extension mapping demonstrated that purB is co-transcribed with an upstream gene (ORF23, or ycfC ) encoding a 22.9 kDa membrane-associated protein of non-essential, but unknown, function unrelated to purine biosynthesis. The purB operon lies between phoP and an ORF expressing an essential function which may correspond to asuE (trmU ). S-AMP lyase was purified to near homogeneity. The purified enzyme is a homotetramer of 50 kDa subunits, has a K m for S-AMP of 3.7 µM and a pH optimum of 7.4-7.6. Author for correspondence: William T. Drabble. Tel: +44 1703 594279. Fax: +44 1703 594459. Keywords: Escherichia coli , purB gene, succinyl-AMP lyase, internal promoter, phoP gene Present address: Department of Molecular Microbiology, University of Southampton, Southampton General Hospital, Southampton SO16 6YD, UK. Present address: Tampa Bay Research Institute, 10900 Roosevelt Blvd, St Petersburg, FL 33716, USA.