Organization of the lexA gene of Escherichia coli and nucleotide sequence of the regulatory region

The product of the lexA gene of Escherichia coli has been shown to regulate expression of the several cellular functions (SOS functions) induced by treatments which abruptly inhibit DNA synthesis. We have cloned and mapped the lexA gene on a small segment of approximately 600 base pairs. The lexA promotor was located by transcription R-loop analysis, and the lexA product of 22,000 daltons was identified by protein synthesis in vitro. An unknown gene was found which directed the synthesis of a protein of 35,000 daltons in a region downstream from the lexA gene. Nucleotide sequence of the regulatory region of the lexA gene was determined. The sequence contained inverted repeats homologous to that of the recA regulatory region. These inverted repeats may be recognized by the lexA protein, because the protein is considered to repress both the genes as a common repressor.

Physical and functional mapping of RP4-TOL plasmid recombinants: analysis of insertion and deletion mutants

Cleavage sites for the restriction endonucleases XhoI, BamHI, HindIII, and EcoRI were mapped on the pTN2 plasmid, a recombinant of TOL and RP4, which specifies the toluene-degrading enzymes in the same way as the wild-type TOL plasmid. The pTN2 plasmid, purified from a strain of Escherichia coli, contained the entire length of the RP4 plasmid (about 54 kilobase pairs [kb]) and the TOL segment (about 56 kb). The TOL segment is inserted at about 12 and 5 kb away from the EcoRI and BamHI cleavage sites of RP4, respectively. Cleavage sites for XhoI, BamHI, HindIII, and EcoRI were also mapped on an insertion mutant, pTN1, and two deletion mutants, pTN81 and pTN9. Analysis of pTN81 and pTN9 allowed estimation of the region of the gene cluster for benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase, as well as the region required for toluate oxygenase activity. Induction of TOL enzymes directed by pTN1 suggested the location and orientation of transcription of the gene cluster for catechol 2,3-oxygenase, 2-hydroxymuconic semialdehyde dehydrogenase, and 2-hydroxymuconic semialdehyde hydrolase. Analysis of strains carrying both pTN9 and a xylR mutant of the TOL plasmid demonstrated that xylR+ is trans dominant over xylR.

Gene expression in vitro of colicin El plasmid

Among eighteen polypeptides synthesized in vitro from colicin El plasmid, one of the major products with a molecular weight of 59,000 was identified as colicin El by its immunological property, molecular size, and biological activity. In addition to this polypeptide, seven other polypeptides reacted with colicin El antiserum. Using EcoRI-cleaved colicin El DNA, a 56,000 dalton polypeptide of truncated colicin El was synthesized, but no polypeptide that reacted with colicin El antiserum was produced from SmaI-cleaved colicin El DNA. This fact indicates that the direction of transcription of colicin El structural gene is from SmaI site to EcoRI site in vitro. The immunity protein of a molecular weight of 14,300 and a component of relaxation proteins of a molecular weight of 64,000 were deduced by comparing the results of the gene expression in vitro of one-half (pAO100) and a quarter (pAO2) of colicin El plasmid. The directions of transcription-translation in the genes on the plasmid were discussed. The colicin El plasmid appears to have at least three transcriptional units.

Isolation of TOL and RP4 recombinants by integrative suppression

We obtained genetic and molecular evidence of non-thermosensitive recombinants of RP4 (Kmr Tcr Cbr/Apr) and the thermosensitive TOL plasmid. As first isolated in Pseudomonas aeruginosa PAO, the recombinant plasmid pTN1 specified noninducible synthesis of TOL enzymes and was transmissible to Escherichia coli on selection for the transfer of kanamycin resistance. The phenotypic expression of TOL genes of pTN1 in E. coli was low and also noninducible. A spontaneous segregant, pTN2, appearing from pTN1, conferred inducible synthesis of TOL enzymes. These plasmids carry all of the TOL determinants as evidenced by the ability of Pseudomonas putida carrying recombinant plasmids to grow on toluene, xylene, and m-toluate. In E. coli the expression of TOL genes with normal regulation (pTN2) appears to be extremely low without induction, and the induced expression is comparable to that with defective regulation (pTN1). The measurement of the molecular weight of pTN2 by electron microscopy gave a value of about 74 X 10(6).

Induction of colicin E1 synthesis in recomination-defective mutants in both the RecBC and RecF pathways

Colicin E1 synthesis was induced in mutants defective in both the RecBC and RecF pathways to the same extent as in Rec(+) strains.

Involvement of NAD in induced synthesis of colicin E1

Escherichia coli K-12 nadC13 (ColE1) was starved for nicotinic acid and cellular NAD levels decreased to less than 10% of the normal. Under these conditions, induction of colicin E1 synthesis decreased to about 1% of the normal value, while 30% of the total protein synthesis remained intact. Addition of nicotinic acid reversed both the ability of the colicin induction and cellular NAD level. Induced replication of colicin E1 DNA was greatly reduced in the NAD-deprived cells.

Requirements of glucose and incubation under static conditions for optimal colicin E1 induction

A rapid rate and large amounts of colicin E1 synthesis were induced by incubating colicinogenic cells without aeration in the presence of glucose. The decrease in ability of colicin induction by aeration was not due to an ample supply of oxygen, but to the simple agitation of the bacterial suspension. Sugars other than glucose that support colicin synthesis were mannose, fructose, glucose-6-phosphate, and mannitol. The effect of sugars in mutants deficient in enzymes of glucose metabolism suggested that some intermediary metabolites between glucose and pyruvate are closely related to the stimulation of colicin synthesis under these conditions. Analyses of deoxyribonucleic acid replication indicated that the induced replication of the colicin E1 plasmid deoxyribonucleic acid occurred even under conditions in which colicin was not actively synthesized.