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

Abstract

Plasmid pAB65, derived from a specialized transducing phage carrying DNA from .apprx. 52 min on the E. coli genome, coded for 2 polypeptides of MW .apprx. 34,000. 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 polypeptide 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 .gamma. 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.