title: Genes aroA and serC of Salmonella typhimurium constitute an operon.
abstract: Genetic analysis of aroA554::Tn10 derivatives of two mouse-virulent Salmonella typhimurium strains, "FIRN" and "WRAY," and of a nonreverting derivative of each constructed for use as a live vaccine, showed the site of the insertion among mapped aroA point mutants. The WRAY live-vaccine strain gave no aro+ recombinants in crosses with aroA point mutations to one side of the insertion, indicating a deletion from Tn10 through the sites of these point mutations. The FIRN live-vaccine strain gave wild-type recombinants with all tested point mutants; it probably has a deletion or inversion extending from Tn10 into aroA but not as far as the nearest point mutation. Some tetracycline-sensitive mutants of aroA554::Tn10 strains required serine and pyridoxine, indicating loss of serC function, and some that were found to be SerC- did not produce gas from glucose, indicating a loss of pfl function. These results show the gene order pfl-serC-aroA, as in Escherichia coli. Ampicillin enrichment applied to pools of tetracycline-sensitive mutants of strains with Tn10 insertions near aroA (i.e., zbj::Tn10 strains) yielded Aro- SerC- Pfl-, Aro- SerC+ Pfl+, and Aro- SerC- Pfl+ mutants but none which were Aro+ SerC-. All of the mutants are explicable by deletions or inversions extending clockwise from zbj::Tn10 into or through an operon comprising serC (promoter-proximal) and aroA. Such an operon was also shown by the identification of two Tn10 insertions causing phenotype Aro- SerC-, each able to revert to Aro+ SerC+ by precise excision. serC corresponds to the open reading frame promoter-proximal to aroA that was identified elsewhere by base sequencing of a cloned aroA segment of S. typhimurium (Comai et al., Science 221:370-371, 1983). Both serine and chorismate are precursors of enterochelin; this may be why serC and aroA are in a single operon.
authors.forename: S K
authors.initials: SK
authors.lastname: Hoiseth
authors.forename: B A
authors.initials: BA
authors.lastname: Stocker
mesh_terms: D001428:Bacterial Vaccines / Q000235:genetics; D001565:Benzoates / Q000378:metabolism; D002874:Chromosome Mapping; D004251:DNA Transposable Elements; D005786:Gene Expression Regulation; D005798:Genes, Bacterial; D008040:Genetic Linkage; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009876:Operon; D012486:Salmonella typhimurium / Q000235:genetics* / Q000276:immunology; D013752:Tetracycline / Q000494:pharmacology; D000637:Transaminases / Q000235:genetics
chemical_list: D001428:Bacterial Vaccines; D001565:Benzoates; D004251:DNA Transposable Elements; D000637:Transaminases; C022393:phosphoserine aminotransferase; D013752:Tetracycline