Analysis of ultraviolet light-induced suppressor mutations in the strain of Escherichia coli K-12 AB1157: an implication for molecular mechanisms of UV mutagenesis

Summary Genetic analysis of histidine independent (His⁴) revertants induced by ultraviolet light in the his-4 E. coli strain AB1157 was carried out: 83% carried ochre (UAA) suppressor mutations and 17% carried back mutations to his ⁺ or (intragenic?) suppressors not detectably separable from his-4. Using the specialized transducing psu 2int ^– phage, which carries supE-supB, it was determined that 87% of the ochre suppressors mapped in the supE-supB region. We were able to deduce that 56% of these affected tRNA ₁ ^Gln by a CAATAA change in the tRNA gene while 31% affected tRNA ₂ ^Gln by TAGTAA change. Although we were unable to deduce the base substitution of the remaining 13%, the results indicated that most of the suppressor mutations are caused by a G:C to A:T transition.These results suggest that the high incidence of supE-supB region suppressor mutation in E. coli by UV would be a reflection of the general feature of UV mutagenesis; i.e. preferential induction of G:C to A:T transition in repairing nonparing DNA lesions.     

Selective effect of p-aminobenzoic acid on mutagenesis: phenotypic analysis of the Arg+-revertants induced by N-nitroso-N-methylurea in the Escherichia coli K-12 AB1157 strain

According to the phenotypic analysis of Arg+ revertants in Escherichia coli K-12 AB1157, the specific mutational changes in bacterial cells under the action of MNU were registered. True and suppressor mutations of four phenotypic groups were noted. The quantity of mutants induced depended upon the DNA and protein syntheses in bacterial cells. The sublethal concentration of para-aminobenzoic acid markedly (10-50 fold) reduced the rate of mutagenic induction and changed the quantity relations of mutants within phenotypic groups.     

Characterization of the E.coli K12 strain AB1157 as impaired in guanine/xanthine metabolism

The widely used E. coli K12 strain AB1157 is impaired in guanine (xanthine) metabolism. Mutants blocked in purine biosynthesis before the stage of inosine monophosphate synthesis do not grow on external guanine or xanthine.The genetic nature of the Gua/Xan lesion is a deletion in the chromosome that covers the pro A gene. The lesion causes reduced uptake of guanine.     

Helium-neon laser preirradiation induces protection against UVC radiation in wild-type E. coli strain K12AB1157

We have observed that preirradiation with a helium-neon laser (632.8 nm) induces protection against UVC radiation in wild-type E. coli strain K12AB1157. The magnitude of protection was found to depend on the helium-neon laser irradiance, exposure time, and period of incubation between helium-neon laser exposure and subsequent UVC irradiation. The optimum values for dose, irradiance and interval between the two exposures were found to be 7 kJ/m(2), 100 W/m(2) and 1 h, respectively. The possible involvement of singlet oxygen in the helium-neon laser-induced protection is also discussed.     

Phenotypic variations in strain AB1157 cultivars of Escherichia coli from different sources.

The purpose of this note is to alert users of Escherichia coli AB1157 and its derivatives to a potentially significant difference in cultivars from various sources. The difference we find is in the ability to host an infection by coliphage 186 after UV irradiation of the host cell.     

Permeability of Escherichia coli K-12 cells to exogenous nucleodepolymerases

The permeability of Escherichia coli cells for exogenous nucleodepolymerases has been studied by an immunoenzyme method. The enzyme ability to penetrate through the bacterial outer membrane and cell wall after 20 min of incubation with culture cells of delayed growth phase has been found.     

Copy numbers of coexisting plasmids in Escherichia coli K-12.

A strain of Escherichia coli K-12 carrying eight compatible and distinguishable plasmids was constructed. The amounts of plasmid DNA (measured as supercoiled molecules) per chromosome in this strain was about equal to the sum of the plasmid DNAs, extracted under controlled conditions, from strains each carrying one of the eight plasmids. Analysis of these DNA preparations showed that each plasmid in the multiplasmid strain was present in the same proportion per chromosome as in the single-plasmid strains. Also the level of phenotypic expression of each plasmid in the multiplasmid strain was the same as in the single-plasmid strains. Each plasmid, therefore, appears to control its own copy number irrespective of the presence of other compatible plasmids.     

Hfr formation by I pilus-determining plasmids in Escherichia coli K-12.

R483, an atypical, I pilus-determining plasmid, and also R144, a typical one, were shown to suppress the DnaA phenotype by integration into the Escherichia coli chromosome.     

Expression of the metA gene of Escherichia coli K-12 in recombinant plasmids

Abstract The expression of the metA gene coding for the first enzyme in the methionine biosynthethic pathway was studied in wild-type and in deregulated strains of Escherichia coli K-12 carrying the gene on multicopy plasmids.
We looked at (a) in vitro activity of the metA product—The enzyme homoserine transsuccinylase (HTS); (b) resistance of cells carrying metA plasmids to the analogue α-methylmethionine which specifically inhibits HTS, and (c) the metA polypeptide in mini cells.
The results indicate that the M _r value of the polypeptide synthesized by the metA gene is 40 000. The synthesis of HTS, even when the metA gene is cloned on a multicopy plasmid, is under the negative control of the regulatory metJ gene.     

Escherichia coli K-12 mutants capable of catabolizing purine nucleosides in the absence of purine nucleoside phosphorylase]

Strains of Escherichia coli K-12 defective in purine nucleoside phosphorylase (pup gene) formed on the medium with inosine as the source of carbon and energy phenotypical reversions for the ability of utilizing inosine as source of carbon or purines. The phenotypical suppression of the purine nucleoside phosphorylase deficiency is the result of the mutations (called pnd), which are mapped on the chromosome of E. coli beyond the region of the structural pup-gene location and have phenotypic manifestation distinct from that of pup+ allele: a) pnd mutants divide into some groups for the ability of utilizing several purine nucleosides, including xantosine that cannot be metabolized by pnd+ strains of E. coli; b) pnd mutations do not restore the ability of purine auxotrophs (pur) defective in purine nucleoside phosphorylase (pup) and adenine phosphoribosyltransferase (apt) to grow on the medium with adenine as the sole source of purines. Cell-free extracts of pnd mutants fail to degrade the guanine nucleosides in the absence of phosphate or arsenate ions. These data (and also the ability of pnd mutants to utilize both purine ribonucleosides and deoxyribonucleosides) seem to indicate that the activities induced by pnd mutations are phosphorylase activities.