title: Suppression of insertions in the complex pdxJ operon of Escherichia coli K-12 by lon and other mutations.
abstract: Complementation analyses using minimal recombinant clones showed that all known pdx point mutations, which cause pyridoxine (vitamin B6) or pyridoxal auxotrophy, are located in the pdxA, pdxB, serC, pdxJ, and pdxH genes. Antibiotic enrichments for chromosomal transposon mutants that require pyridoxine (vitamin B6) or pyridoxal led to the isolation of insertions in pdxA, pdxB, and pdxH but not in pdxJ. This observation suggested that pdxJ, like pdxA, pdxB, and serC, might be in a complex operon. To test this hypothesis, we constructed stable insertion mutations in and around pdxJ in plasmids and forced them into the bacterial chromosome. Physiological properties of the resulting insertion mutants were characterized, and the DNA sequence of pdxJ and adjacent regions was determined. These combined approaches led to the following conclusions: (i) pdxJ is the first gene in a two-gene operon that contains a gene, temporarily designated dpj, essential for Escherichia coli growth; (ii) expression of the rnc-era-recO and pdxJ-dpj operons can occur independently, although the pdxJ-dpj promoter may lie within recO; (iii) pdxJ encodes a 26,384-Da polypeptide whose coding region is preceded by a PDX box, and dpj probably encodes a basic, 14,052-Da polypeptide; (iv) mini-Mud insertions in dpj and pdxJ, which are polar on dpj, severely limit E. coli growth; and (v) three classes of suppressors, including mutations in lon and suppressors of lon, that allow faster growth of pdxJ::mini-Mud mutants can be isolated. A model to account for the action of dpj suppressors is presented, and aspects of this genetic analysis are related to the pyridoxal 5'-phosphate biosynthetic pathway.
authors.affiliation: Department of Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611.
authors.forename: H M
authors.initials: HM
authors.lastname: Lam
authors.forename: E
authors.initials: E
authors.lastname: Tancula
authors.forename: W B
authors.initials: WB
authors.lastname: Dempsey
authors.forename: M E
authors.initials: ME
authors.lastname: Winkler
mesh_terms: D049069:ATP-Dependent Proteases; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000166:cytology / Q000235:genetics*; D029968:Escherichia coli Proteins; D005816:Genetic Complementation Test; D006360:Heat-Shock Proteins; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009154:Mutation; D009876:Operon / Q000235:genetics*; D049070:Protease La; D011736:Pyridoxine / Q000235:genetics*; D012697:Serine Endopeptidases / Q000235:genetics; D013489:Suppression, Genetic; D014166:Transferases
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; C073125:acpS protein, E coli; D014166:Transferases; D049069:ATP-Dependent Proteases; D012697:Serine Endopeptidases; C483567:Lon protein, E coli; D049070:Protease La; D011736:Pyridoxine