Location on the Escherichia coli Genome of a Gene Specifying O-Acetylserine (Thiol)-lyase

Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK ABSTRACT The plasmid pAB65, derived from a specialized transducing phage carrying DNA from about 52 min on the Escherichia coli genome, coded for two polypeptides of M r approx. 34000. The expression of one was regulated by cyst(e)ine and the cysB gene product and the other by the cysB gene product only. One of these polypeptides was a subunit of O -acetylserine (thiol)-lyase (EC 4.2.99.8 ); the other, associated with the E. coli membrane, was the N-terminus of the product of the ben gene. The pattern of peptide synthesis directed by plasmids carrying smaller DNA fragments indicated that the gene for O -acetylserine (thiol)-lyase was transcribed clockwise. The spectrum, amino acid composition and subunit number of the enzyme were determined. The enzyme appears homologous with the Salmonella typhimurium cysK gene product. This provides further evidence for the inversion of this region of the genome. Present address: Departamento de Bioquímica, Facultad de Medicina, Universidad de Oviedo, Oviedo, Spain Present address: Agricultural Research Council Institute for Research on Animal Diseases, Compton, Nr Newbury, RG16 ONN, UK Present address: Centro de Biologia Molecular, Universidad Autónoma de Madrid, Canto Blanco, Madrid-34, Spain