lexA dependent recombination in uvrD strains of Escherichia coli

Mutation of the uvrD gene of Escherichia coli is associated with an increased capacity for genetic recombination. The hyper-recombination effect is abolished by an additional mutation in lexA that limits synthesis of RecA protein and other gene products regulated by LexA repressor, and is not restored when increased synthesis of RecA protein is facilitated by a recAoc mutation. The viability of uvrD lexA strains is reduced and revertants selected on the basis of improved growth fall into three categories: those that are lexA+, or carry another mutation in lexA that directly suppresses the lexA defect; recA mutants that have lost the capacity for recombination altogether; and a third class which carry a mutation that is not in lexA or recA and which restores the hyper-rec phenotype but does not otherwise suppress the lexA defect. These results indicate that the hyper-recombination effect of a uvrD mutation is an induced response catalysed by RecA protein and at least one other lexA regulated activity.     

Further characterization of SOS system induction in recBC mutants of Escherichia coli

Expression of several SOS functions such as induction of lambda prophage, inhibition of cell division and induction of both umuC and recA genes after UV-irradiation, nalidixic acid or mitomycin C addition was studied in an RecBC- mutant. UV-irradiation and mitomycin C induced all SOS functions studied in the RecBC- cells but at a lower level and delayed with respect to the wild-type strain. On the contrary, nalidixic acid was unable to trigger any of these SOS functions. In the RecBC- mutant, adenine only had a stimulating effect on the amplification of RecA protein synthesis following UV-irradiation. Nevertheless, in the wild-type strain the stimulating effect occurred in all SOS functions studied following UV-irradiation as well as in the amplification of RecA protein synthesis by nalidixic acid but not in the other SOS functions triggered by this compound. Furthermore, adenine produced a decrease in the mitomycin C-mediated induction of all SOS functions studied in both RecBC- and wild-type strains.     

Induction of Phage Production in the Lysogenic Escherichia coli by Hydroxyurea

1) Hydroxyurea, a reversible DNA synthesis inhibitor, was used to study the mechanism of prophage λ induction in Escherichia coli K12. Induction of prophage was judged on two criteria: increase of phage-producing cells and loss of colony-forming ability of the cells. 2) Hydroxyurea induced an increase of phage-producing cells only in lysogenic strains known to be inducible with ultraviolet irradiation for prophage development and not in strains such as E. coli K12 (λind^–) or E. coli K12 recA (λ⁺). 3) When protein synthesis was inhibited, hydroxyurea did not increase phage-producing cells of lysogenic strains; it showed a bacteriocidal effect on lysogenic recA⁺ strains, but not on nonlysogenic strains. 4) The sensitivity of E. coli K12 recA to hydroxyurea was independent of whether or not the cells were lysogenic. 5) From the results it is suggested that certain steps leading to loss of colony-forming ability (i.e. prophage induction) do not require de novo protein synthesis but require the presence of the host recA⁺ gene.     

Transducing lambda phages with Escherichia coli genes

The paper presents data on transducing lambdoid phages containing Escherichia coli genes. The major genetic techniques for isolating transducing phages (in vivo) are outlined. A combined table of best-studied transducing phages obtained by the methods of molecular genetics and genetic engineering lists phages genotype & basic literature references for the phages and their derivatives. The chromosome fragments of E. coli inserted in phage DNA are separately specified. Another table presents information about phages carrying E. coli fused operons and genes. The paper also provides detailed physical maps of three regions of the E. coli chromosome. The bibliography contains 300 items.     

Prophage Induction in Lysogenic Escherichia coli with N-Nitroso Compounds and Derivatives

Prophage induction in lysogenic Escherichia coli W1709 (iota) was determined for 29 N-nitroso compounds, 13 of their denitrosated derivatives, and 7 hydroxylamino and hydrazino analogues of nitrosamines. Minimal inducing concentrations of 0.1 to 2.0 mug/ml were demonstrated for eight nitrosamidines, and concentrations of 0.5 to 25.0 mug/ml were shown for six nitrosamides. Weak inducing activities were found with N,N-diethylhydroxylamine oxalate and N-methyl-N-phenylhydrazine sulfate, derivatives of inactive N-nitrosodiethylamine and N-nitrosomethylphenylamine, respectively. Inactive compounds including N-methyl-N-nitroso-p-toluenesulfonamide, 11 nitrosamines, 3 N, N'-dialkyl substituted-N-nitrosoureas, 13 denitrosated derivatives, and 5 hydroxylamino and hydrazino analogues of nitrosamines are listed. Since 7 of the 14 prophage-inducing nitrosamidines and nitrosamides reported thus far have carcinostatic activity in rodent tumor systems, it is concluded that the induction test may provide a useful screen for the detection of potential antitumor compounds. The induction test may also be useful for the detection of responsive N-nitroso compounds which may be potential toxicological hazards in the environment since, of the six active nitrosamides, five have already been reported to produce mutagenic and carcinogenic effects, four produce chromosomedamaging effects, and two produce teratogenic effects. Use of the prophage induction system for detection of biologically active intermediates formed by N-nitroso compounds under physiological conditions is considered.     

Gamma-ray induction of deoxyribonucleic acid synthesis in temperature-sensitive DNA initiation mutants of Escherichia coli

DNA synthesis was followed after gamma-ray irradiation of several different temperature-sensitive mutants with defects in the initiation process. The results indicate that only dnaA and dnaI mutants show induction of supplementary DNA synthesis after gamma-ray irradiation. The induction of DNA synthesis by gamma-ray irradiation was also shown to be recA+ dependent in the dna5 mutant.     

Different sensitivity of autolytic deficient Escherichia coli mutants to the mode of induction

Abstract By a comparison of the rate øX174 gene E product (gpE)-induced autolysis of Escherichia coli RM4101 and its autolysis deficient mutant strains RK232, RK238 and RK316, it was shown that gpE-induced autolysis differs from autolysis induced by EDTA or moenomycin. Subclones of these strains which could no longer be lysed by gpE can be lysed by EDTA shock treatment or moenomycin at almost normal rates. GpE seems to induce only partially the activity of the autolytic system of E. coli.     

Analysis of the Escherichia coli Alp phenotype: heat shock induction in ssrA mutants

The major phenotypes of lon mutations, UV sensitivity and overproduction of capsule, are due to the stabilization of two substrates, SulA and RcsA. Inactivation of transfer mRNA (tmRNA) (encoded by ssrA), coupled with a multicopy kanamycin resistance determinant, suppressed both lon phenotypes and restored the rapid degradation of SulA. This novel protease activity was named Alp but was never identified further. We report here the identification, mapping, and characterization of a chromosomal mutation, faa (for function affecting Alp), that leads to full suppression of a Deltalon ssrA::cat host and thus bypasses the requirement for multicopy Kan(r); faa and ssrA mutants are additive in their ability to suppress lon mutants. The faa mutation was mapped to the C terminus of dnaJ(G232); dnaJ null mutants have similar effects. The identification of a lon suppressor in dnaJ suggested the possible involvement of heat shock. We find that ssrA mutants alone significantly induce the heat shock response. The suppression of UV sensitivity, both in the original Alp strain and in faa mutants, is reversed by mutations in clpY, encoding a subunit of the heat shock-induced ClpYQ protease that is known to degrade SulA. However, capsule synthesis is not restored by clpY mutants, probably because less RcsA accumulates in the Alp strain and because the RcsA that does accumulate is inactive. Both ssrA effects are partially relieved by ssrA derivatives encoding protease-resistant tags, implicating ribosome stalling as the primary defect. Thus, ssrA and faa each suppress two lon mutant phenotypes but by somewhat different mechanisms, with heat shock induction playing a major role.     

Differences in host controlled reactivation of lambdoid and T phages

Summary Phages 434, T4, T5 and T7 are studied with regard to host controlled reactivation of damage produced by UV or photodynamic action sensitized by thiopyronine. Repair of 434 phages proceeds under control of both hcr and rec genes. UV irradiated T5 and T7 phages are reactivated under control of the host's hcr genes only. If these phages are inactivated by photodynamic action they are reactivated not at all. T4 phages inactivated by both treatments are also refractory to host controlled reactivation. These differences might reflect different degrees of autarchy and different abilities of phage DNAs to serve as substrate for recombination enzymes of the host.These results were presented in an abstracted version at the V. International UV colloquium Grundlagen der UV-Wirkung, Kühlungsborn, DDR, in October 1969. The experiments with T5 were done by Mrs. E. Marx.     

Flagellar assembly mutants in Escherichia coli

Genetic and biochemical analysis of mutants defective in the synthesis of flagella in Escherichia coli revealed an unusual class of mutants. These mutants were found to produce short, curly, flagella-like filaments with low amplitude ( approximately 0.06 mum). The filaments were connected to characteristic flagellar basal caps and extended for 1 to 2 mum from the bacterial surface. The mutations in these strains were all members of one complementation group, group E, which is located between his and uvrC. The structural, serological, and chemical properties of the filament derived from the mutants closely resemble those of the flagellar hook structure. On the basis of these properties, it is suggested that these filaments are "polyhooks", i.e., repeated end-to-end polymers of the hook portion of the flagellum. Polyhooks are presumed to be the result of a defective cistron which normally functions to control the length of the hook region of the flagellum.     

Lysogenic Conversion of Pasteurella by Escherichia coli Bacteriophage P1 CM

Bacteriophage P1 CM can convert Pasteurella pestis or P. pseudotuberculosis to chloramphenicol resistance and phage restriction, but no viable phage was induced from converted Pasteurella strains.     

Prophage Induction in Lysogenic Escherichia coli with Simple Hydroxylamine and Hydrazine Compounds

The prophage-inducing capability of hydroxylamine sulfate and 36 of its derivatives, and of hydrazine dihydrochloride and dihydrazine sulfate and 43 of their derivatives, was determined in Escherichia coli W1709 (lambda). Maximal nontoxic concentrations up to 1 mg/ml were tested. Hydroxylamine sulfate was active at 2.5 mug/ml and the following 17 derivatives were active at concentrations ranging up to 500 mug/ml: alpha-naphthylhydroxylamine, N-hydroxy-2-aminofluorene, oxamyl hydroxamic acid, O-carbamoyl hydroxylamine (isohydroxyurea), N-hydroxyurethane, N-methylhydroxylamine HCl, salicylhydroxamic acid, oxalohydroxamic acid, methoxyamine HCl, ethoxyamine HCl, N, N-diethylhydroxylamine oxalate, formaldoxime, formamidoxime, acetohydroxamic acid, acetaldoxime, acetone oxime, and hydroxyguanidine sulfate. Hydrazine dihydrochloride and dihydrazine sulfate were effective inducers at 5.0 and 2.5 mug/ml, respectively, and the following nine derivatives of them were active at concentrations ranging up to 500 mug/ml: phthalic acid hydrazide, phenylhydrazine HCl, p-nitrophenylhydrazine, p-chlorophenylhydrazine HCl, formylhydrazine, carbohydrazide, semicarbazide HCl, 1-methyl-1-phenyl-hydrazine sulfate, and acetic acid hydrazide. Nineteen hydroxylamine and 34 hydrazine derivatives were ineffective as inducers. Application of the prophage-induction system as a tool for detection of responsive hydroxylamino and hydrazino compounds which may be potential toxicological hazards in the environment is discussed.