Construction and use of pyr::lac fusion strains to study regulation of pyrimidine biosynthesis in Salmonella typhimurium.

The technique developed by Rosenfeld and Brenchley [J Bacteriol 144, 848-851 (1980)] has been used to introduce Mu d1 (Apr lac) into Salmonella typhimurium for purposes of constructing pyr::lac fusion strains. A stable pyrB::lac fusion mutant was subsequently derived and used for the genetic characterization of the pyrB gene. The direction of transcription of pyrB was determined to be counterclockwise on the S. typhimurium linkage map and argI was shown to be located clockwise of pyrB. Mutants altered in the regulation of expression of pyrB were isolated and two of the isolates chosen for further study were tentatively categorized as promoter or operator mutants.