Studies on radiation-sensitive mutants of E. coli. I. Mutants defective in the repair synthesis

Influence of a uvrD mutation on survival and repair of X-irradiated Escherichia coli K-12 cells

The presence of a uvrD mutation increased the X-ray sensitivities of E. coli wild-type and polA strains, but had no effect on the sensitivities of recA and recB strains, and little effect on a lexA strain. Incubation of irradiated cells in medium containing 2,4-dinitrophenol or chloramphenicol decreased the survival of wild-type and uvrD cells, but had no effect on the survival of recA, recB and lexA strains. Alkaline sucrose gradient sedimentation studies indicated that the uvrD strain is deficient in the growth-medium-dependent (Type III) repair of DNA single-strand breaks. These results indicate that the uvrD mutation inhibits certain rec+lex+-dependent repair processes, including the growth-medium-dependent (Type III) repair of X-ray-induced DNA single-strand breaks, but does not inhibit other rec+lex+-dependent processes that are sensitive to 2,4-dinitrophenol and chloramphenicol.

Plasmid (pKM101)-mediated enhancement of repair and mutagenesis: dependence on chromosomal genes in Escherichia coli K-12

The drug resistance plasmid pKM101 plays a mojor role in the Ames Salmonella/microsome carcinogen detecting system by enhancing chemical mutagenesis. It is shown that in Escherichia coli K-12 the plasmid pKM101 enhances both spontaneous and methyl methanesulfonate-caused reversion of an ochre mutation, bacterial survival after ultraviolet irradiation, and reactivation of ultraviolet-irradiated lambda in unirradiated cells. All these effects are shown to be dependent on the recA+ lexA+ genotype but not on the recB+ recC+ or recF+ genotypes. The recA lexA-dependence of the plasmid-mediated repair and mutagenesis suggests an interaction with the cell's inducible error-prone repair system. The presence of pKM101 is shown to cause an additional increase in methyl methanesulfonate mutagenesis in a tif mutant beyond that caused by growth at 42 degrees. The presence of the plasmid raises the level of the Weigle-reactivation curve for the raactivation of ultraviolet-irradiated lambda in E. coli and causes a shif of the maximum to a higher UV fluence. These observations suggest that pKM101 does not exert its effects by altering the regulation of the cell's error-prone repair system but rather by supplying a mechanistic component or components.

Misrepair of overlapping daughter strand gaps as a possible mechanism for UV induced mutagenesis in UVR strains of Escherichia coli: a general model for induced mutagenesis by misrepair (SOS repair) of closely spaced DNA lesions

It has been previously reported that an inducible form of post-replication repair appeared to be required for UV induced mutagenesis in a uvrA strain of Escherichia coli. It is shown here that the numbers of daughter strand gaps requiring inducible repair were similar to the numbers calculated to be overlapping one another in opposite daughter chromosomes. An estimation of survival with no repair of these gaps resembled the survival predicted with no mutagenesis. It is the thus proposed that inducible post-replication repair causes mutagenesis by the repair of overlapping daughter strand gaps. A general model for induced mutagenesis is presented. It is proposed that (a) some DNA lesions introduced by any DNA damaging agent may be close enough to interfere with constitutive repair replication of each other, (b) these lesions induce a repair system (SOS repair) which involves the recA+ lexA+ and polC+ genes (c) repair and concomitant mutagenesis occurs during repair replication by the insertion of mismatched bases opposite the noncoding DNA lesions.

Degradation, metabolism and toxicity of synthetic pyrethroids

Synthetic pyrethroidal compounds undergo biodegradation in mammals both oxidatively and hydrolytically, and depending on the type of compound, either of the pathways may predominate. Thus, (+) - or (+/-) -trans isomers of the chrysanthemumate ester of primary alcohols such as fenothrin, furamethrin, proparthrin, resmethrin, and tetramethrin (and possibly permethrin, too) are metabolized mainly through hydrolysis of the ester linkage, with subsequent oxidation and/or conjugation of the component alcohol and acid moieties. On the other hand, the corresponding (+)-cis enantiometers and chrysanthemumate of secondary alcohols like allethrin are resistant to hydrolytic attack, and biodegraded via oxidation at various sites of the molecule. These rapid metabolic degradations, together with the presumable incomplete absorption from the gastrointestinal tract, would generally contribute to the low acute toxicity of synthetic pyrethroids. These compounds are neither skin irritants nor skin sensitizers, and inhalation toxicity as well as dermal toxicity are fairly low. Neither is teratogenic in rats, mice, and/or rabbits or mutagenic on various bacterial strains. Subacute and chronic feeding of higher amounts of the compounds to rats invariably causes some histopathological changes in liver; however, these are neither indicative nor suggestive of tumorigenicity. Based on existing toxicological information, the present recommended use patterns might afford sufficient safety margin on human population. However, in extending usage to agricultural pest control, much more extensive investigations should be forthcoming from both chemical and biological aspects, since there is scant information on the fate of these pyrethroids in the environment. Also several of the compounds may be very toxic to certain kinds of fish and arthropods.

Isolation and genetic analysis of amber uvrA and uvrB mutants

Genetic properties of amber uvrA and uvrB mutants of Escherichia coli K-12 are described. The isolation of three amber uvrA and two amber uvrB mutants indicates that the products of these genes are proteins.

Carcinogen-induced DNA repair in nucleotide-permeable Escherichia coli cells. Analysis of DNA repair induced by the carcinogens N-acetoxy-N-2-acetylaminofluorene and 7-bromomethyl-benz(a)anthracene

Upon exposure to the carcinogens N-acetoxy-N-2-acetylaminofluorene and 7-bromomethyl-benz[a]anthracene, which bind covalently to DNA, ether-permeabilized (nucleotide-permeable) Escherichia coli wild-type cells responded with DNA excision repair. This repair was missing in mutants carrying defects in genes uvrA, uvrB and uvrC, whereas it was present in uvrD and several rec mutants. Enzymic activities involved were identified by measuring repair polymerization and size reduction of denatured DNA. 1. An easily measurable effect in E. coli wild-type cells was carcinogen-induced repair polymerization. When initiated by N-acetoxy-N-2-acetylaminofluorene or 7-bromomethyl-benz[a]anthracene, it depended upon an ATP-requiring step; CTP, GTP or UTP did not substitute for ATP. DNA repair synthesis was inhibited by p-chloromercuribenzoate and quinacrine. In uvrA, uvrB and uvrC mutants no carcinogen-stimulated DNA synthesis could be detected, indicating that steps involved in pyrimidine dimer excision are also involved in chemorepair. In recA, recB and recC mutant cells, repair synthesis was stimulated by the carcinogens to a normal extent. This evidence excludes the ATP-dependent recB,C deoxyribonuclease and recA gene products as playing an important role in carcinogen-induced excision repair. polA1 cells showed drastically reduced levels of rapair polymerization, indicating that DNA polymerase I is the main polymerizing enzyme. 2. As determined by DNA size reduction in alkaline sucrose gradients, the arylalkylating carcinogens caused endonucleolytic cleavage of endogenous DNA in wild-type cells. This incision step was most effectively performed in the presence of ATP; UTP, CTP and GTP were only slightly effective. Incision was inhibited by p-chloromercuribenzoate and quinacrine. When exposed to the arylalkylating carcinogens, uvrA, uvrB and uvrC mutant cells did not perform the incision step in the presence of ATP, suggesting the involvement of the respective gene products in the initiation of chemorepair.

Genetic control of multiple pathways of post-replicational repair in uvrB strains of Escherichia coli K-12

The effect of the recA, uvrD, exrA, and recB mutations and of post-irradiation treatment with chloramphenicol on the survival and post-replication repair after ultraviolet irradiation of uvrB strains of Escherichia coli K-12 was examined. Each of these mutations or treatments was found to decrease survival and the extent of repair. The interactions of the inhibitory effects of the uvrD, exaA, and recB mutations and chloramphenicol treatment were determined by examining the survival and repair characteristics of the several multiple mutants. The survival results suggest that the post-replication repair process in uvrB strains may be subdivided into at least five different branches. These include three branches that are blocked by the exrA, recB, or uvrD mutation, a fourth branch that is blocked by any of these mutations and is also sensitive to chloramphenicol treatment, and at least one additional branch that is not sensitive to either of these mutations or to chloramphenicol treatment. The extent of post-replicational repair observed with each of the strains is in general agreement with the pathways postulated on the basis of the survival data, although there are several apparent exceptions to this correlation.

DNA repair in Proteus mirabilis. III.Survival, dimer excision, and UV reactivation in comparison with Escherichia coli K12

Measurements of UV sensitivity of wildtype cells (wt) and UV senistive mutants of E. coli and P. mirabilis suggest that the increased sensitivity of P. mirabilis (wt) is due either to incomplete repair of DNA lesions or to additive lethality probably as a result of UV induction of defective phage(s) present in P. mitabilis (Taubeneck, 1967). Direct estimates of the rate of pyrimidine dimer excision and a comparison of the UV reactivation capacity of E. coli and P. mirabilis for the temperate phages lambda and pi 1, respectively, support this conclusion.

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 lambda 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 (lambdaind-) or E. coli K12 recA (lambda+). 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.

Escherichia coli mutants uvr D and uvr E deficient in gene conversion of lambda-heteroduplexes

Calcium-treated cells of E. coli K-12 C600 were transfected with lambda-heteroduplex DNA carrying the marker cIts857 in one strand and wildtype in the other. In single burst analyses of the phage progeny, 72-79% of the bursts were "pure" bursts containing either exclusively wildtype phage or exclusively mutant phage, indicating that conversion of the cIts857/+ mismatch to a homoduplex structure prior to replication occurred with this frequency. The r-strand1 appears to be "preferred", since pure bursts of progeny with the r-strand genotype were almost twice as frequent as those with the l-strand genotype. Examination of the conversion frequency of a number of rec and uvr E. coli mutants showed that the mutants uvr D and UVR E are deficient in mismatch repair. Conversion is reduced in the former by a factor of 2 and in the latter by a factor of 3.

Phileomycin-induced lethality and DNA degradation in Escherichia coli K12

The cell lethality and DNA fragmentation caused by phleomycin (PM) were studied in E. coli K12 strains with special reference to the effects of repair or recombination deficiences and metabolic inhibitors. (1) Unlike excision-defective derivatives of E. coli B, uvrA, uvrB, and uvrC mutants of strain K12 showed no peculiarities compared with wild type in regard to cell survival. Likewise, mutant alleles at uvrD and polA loci had no effect. In contrast, rec mutants were more sensitive to PM-killing than were rec+ strains. (2) PM-induced strand breakage in DNA was observed in all strains tested including the above-mentioned mutants. There was no significant distinction between the uvr mutants and the wild type strain, indicating that the uvr-endonuclease was not responsible for the strand breaks. Involvement of endonuclease I was also ruled out. (3) At least some of the PM-induced breaks were repairable. (4) PM-induced lethality and strand breakage were totally dependent on energy supply. Inhibition of protein synthesis resulted in a partial and parallel suppression of the two effects. Our results suggest that the lethality is due to DNA strand breakage and the repair of such damage is postulated to be controlled by rec genes.

Proposed mechanism of bacteriophage lambda induction: acquisition of binding sites for lambda repressor by DNA of the host

Interference with the in vitro binding of lambda phage repressor to lambda operator DNA was observed when Escherichia coli DNA containing the following lesions was present in the reaction mixture: (a) DNA with single-strand breaks from pancreatic DNase (nicked DNA); (B) DNA isolated from thymine-straved cells; (c) DNA from ultraviolet-treated cells; (d) DNA of mitomycin-treated cells; and (e) DNA from a temperature-sensitive ligase mutant after 1 hr at 42 degrees. Normal E. coli DNA did not interfere. Binding of lambda cIing-minus repressor to operator DNA was not affected by E. coli DNA with lesions. DNAs from cells treated with increasing doses of mitomycin were proportionately more effective in competition for repressor, suggesting increasing binding sites per unit of DNA. A general model of virus induction is proposed, based on binding affinity of ultraviolet-sensitive repressors for single-strand breaks in the host DNA. The model is extended also to the presumptive repressor of cell division.

Excision of pyrimidine dimers in normal and T4-infected Escherichia coli: effect of polA and other mutations

Strains carrying both polA1 and recBts1 mutations, which are defective in DNA polymerase I and have thermolabile exonuclease V (the recBC enzyme), are viable at 30 degrees C but not at 42 degrees C. These mutants exhibit almost normal rate of dimer excision in vivo even at the restrictive temperature. Similar results were obtained with other polA minus strains. We have also investigated effect of host and phage mutations on excision of dimers in T4-infected cells. Only a small amount of dimer is excised in T4v-1-infected cells whereas an extensive and selective release of dimers takes place in T4D-infected cells. Other phage mutations, including mutations in gene 43 and gene 30, do not affect excision of dimers in infected cells.

Inhibitory effect of U.V. -irradiation on the formation of twisted circular lambda DNA

Ultra-violet irradiation of lambda phage results in an inhibition of conversion of lambda DNA in host cells from the initial linear form to twisted circular form. The formation of open circular lambda DNA in vitro (formation of Hershey's circle) was quite resistant to the irradiation. The occurrence of denaturation of ultraviolet irradiation was detected in lambda DNA.

Recovery of phage lambda from ultraviolet damage

Recovery of phage lambda from ultraviolet damage can occur, in the dark, through three types of repair processes as defined by microbiological tests: (1) host-cell reactivation, (2) prophage reactivation, and (3) UV reactivation. This paper reviews the properties of the three repair processes, analyzes their dependence on the functioning of bacterial and phase genes, and discusses their relationship. Progress in the understanding of the molecular mechanisms underlying the three repair processes has been relatively slow, particularly for UV reactivation. It has been shown that host-cell reactivation is due to pyrimidine dimer excision and that prophage reactivation is due to genetic recombination (prereplicative). We provide evidence showing that neither of these mechanisms accounts for UV reactivation of phage lambda. Furthermore, UV reactivation differs from the other repair processes in that it is inducible and error-prone. Whether UV-damaged bacterial DNA is subject to a similar repair process is still an open question.

Fate of donor deoxyribonucleic acid in a highly transformation-deficient strain of Haemophilus influenzae

A transformation-deficient strain of Haemophilus influenzae (efficiency of transformation 10(4)-fold less than that of the wild type), designated TD24, was isolated by selection for sensitivity to mitomycin C. In its properties the mutant was equivalent to recA type mutants of Escherichia coli. The TD24 mutation was linked with the str-r marker (about 30%) and only weakly linked with the nov-r2.5 marker. The uptake of donor deoxyribonucleic acid (DNA) was normal in the TD24 strain, but no molecules with recombinant-type activity (molecules carrying both the donor and the resident marker) were formed. In the mutant the intracellular presynaptic fate of the donor DNA was the same as that in the transformation-proficient (wild-type) strain, and the radioactive label of the donor DNA associated covalently with the recipient chromosome in about the same quantity as in the wild type. However, many fewer donor atoms were associated with segments of the mutant's recipient chromosome as compared with segments of the wild-type chromosome. In the mutant the association was accompanied by complete loss of donor marker activity. The lack of donor marker activity of the donor-recipient complex of DNA isolated from the mutant was not due to lack of uptake of the complex by the second recipient and its inability to associate with the second recipient's chromosome. Because the number of donor-atom-carrying resident molecules was higher than could be accounted for by the lengths of presynaptic donor molecules, we favor the idea that the association of donor DNA atoms with the mutant chromosome results from local DNA synthesis rather than from dispersive integration of donor DNA by recombination.

Phenethyl alcohol resistance in Escherichia coli. 3. A temperature-sensitive mutation(dnaP) affecting DNA replication

A temperature-sensitive DNA replication mutant of E. coli K-12 was isolated among the mutants selected for phenethyl alcohol resistance at low temperatures. This mutation, designated as dnaP18, affects sensitivity of the cell to phenethyl alcohol, sodium deoxycholate and rifampicin, presumably due to an alteration in the membrane structure. At high temperatures (e.g., 42 degrees ), synthesis of DNA, but not RNA or protein, is arrested, leading to the formation of "filaments" in which no septum formation is apparent. Nucleoids observed under electron microscope seem to become dispersed and DNA fibrils less condensed, which may explain the loss of viability under these conditions. Genetic analyses, including reversion studies, indicate that a recessive dnaP mutation located between cya and metE on the chromosome is responsible for both alterations of the membrane properties and temperature sensitivity. The dnaP18 mutation does not affect growth of phage T4 or lambda under conditions where host DNA replication is completely inhibited. Kinetic studies of DNA replication and cell division in this mutant after the temperature shift from 30 to 42 degrees , and during the subsequent recovery at 30 degrees , accumulated evidence suggesting that DNA replication comes to a halt at 42 degrees upon completion of a cycle already initiated before the temperature shift. Since the recovery of DNA synthesis after exposure to 42 degrees does not depend on protein or RNA synthesis or other energy-requiring processes, the product of the mutant dnaP gene appears to be reversibly inactivated at 42 degrees . Taken together with the recessive nature of the present mutation, it was suggested that one of the membrane proteins involved in initiation of DNA replication is affected in this mutant.

Involvement of recA and exr genes in the in vivo inhibition of the recBC nuclease

When Escherichia coli cells are gamma irradiated they degrade their deoxyribonucleic acid (DNA). The DNA of previously gamma-irradiated T4 phage is also degraded in infected cells. The amount of degradation is not only dependent on the dose but also on the genotype of the cell. The amount of degradation is less in cells carrying a recB or a recC mutation, suggesting that most of the DNA degradation is due to the recB(+) and recC(+) gene product (exonuclease V). In some strains a previous dose of ultraviolet (UV) light followed by incubation renders the cells resistant to DNA degradation after gamma irradiation. We have shown this inhibition to take place for infecting T4 phage also. By using six strains of E. coli selected for mutations in the genes recA, exr (or lex), and uvrB, we have been able to show that the preliminary UV treatment produces no change in recA and exr cells for both endogenous DNA degradation and the degradation of infecting irradiated T4 phage DNA, i.e., inhibition was not detected in these strains. On the other hand, wild-type cells and strains carrying mutations of uvrB show inhibition in both types of experiments. Because the recA gene product and the exr(+) (lex(+)) gene product are necessary for the induction of prophage, it is possible that the phenomenon of inducible inhibition requires recA(+) and exr(+) presence. One interpretation of these results is that an inducible inhibitor may be controlled by the exr gene.

An endonuclease from Escherichia coli that acts preferentially on UV-irradiated DNA and is absent from the uvrA and uvrB mutants

At least two endonucleolytic activities that preferentially incise ultraviolet (UV)-irradiated DNA exist in extracts of E. coli. These two activities can be separated by phosphocellulose chromatographic fractionation. The subject of this paper is one of these activities, which elutes from phosphocellulose with 0.25 M potassium phosphate, pH 7.5. This endonucleolytic activity specific for UV-irradiated DNA is absent from partially purified extracts of uvrA and uvrB mutants, which are defective in excision of pyrimidine dimers, but is present in normal amounts in the uvrC excision-defective mutant. The enzyme binds very tightly and specifically to UV-irradiated DNA. Binding can be prevented by prior treatment of the irradiated DNA with photoreactivating enzyme. This binding activity is absent in uvrA and uvrB mutants, but present in uvrC and uvrD mutants.

In vitro repair of UV-irradiated Micrococcus luteus bacteriophage N1 transfecting DNA

Calcium-treated UV-sensitive, host cell reactivation(-) strains of Micrococcus luteus are infected with UV-irradiated N1 DNA. In strains lacking UV endonuclease, in vitro treatment of the irradiated DNA results in transfection enhancement.

Involvement of the recB-recC nuclease (exonuclease V) in the process of x-ray-induced deoxyribonucleic acid degradation in radiosensitive strains of Escherichia coli K-12

The ras, polA, exrA, recA, and uvrD3 strains of Escherichia coli K-12 degrade their deoxyribonucleic acid more extensively than wild-type strains after X irradiation. The relationship of the recB-recC nuclease (exonuclease V) to the degradation process in these strains was determined by comparing the degradation response of the original strains with that of strains containing an additional recB21 or recC22 mutation. The initial rate of degradation in ras, polA12, exrA, and recA13 strains after an exposure of 20 to 30 kR was reduced more than 10-fold by the presence of an additional recB21 or recC22 mutation. The extent of degradation in these irradiated strains after 90 to 120 min of incubation was reduced two- to fivefold. In the uvrD3 strain, a recC22 mutation caused a fourfold decrease in initial degradation rate and reduced the extent of degradation after 90 min of incubation by a factor of 1.6. The results are consistent with the statement that the degradation process is normally dependent on exonuclease V activity. However, the observation that 10 to 30% degradation always occurred even in recB or recC strains, which lack this enzyme, suggests that alternative degradation mechanisms exist.

Ultraviolet-sensitive mutator strain of Escherichia coli K-12

An ultraviolet (UV)-sensitive mutator gene, mutU, was identified in Escherichia coli K-12. The mutation mutU4 is very close to uvrD, between metE and ilv, on the E. coli chromosome. It was recessive as a mutator and as a UV-sensitive mutation. The frequency of reversion of trpA46 on an F episome was increased by mutU4 on the chromosome. The mutator gene did not increase mutation frequencies in virulent phages or in lytically grown phage lambda. The mutU4 mutation predominantly induced transitional base changes. Mutator strains were normal for recombination and host-cell reactivation of UV-irradiated phage T1. They were normally resistant to methyl methanesulfonate and were slightly more sensitive to gamma irradiation than Mut(+) strains. UV irradiation induced mutations in a mutU4 strain, and phage lambda was UV-inducible. Double mutants containing mutU4 and recA, B, or C were extremely sensitive to UV irradiation; a mutU4 uvrA6 double mutant was only slightly more sensitive than a uvrA6 strain. The mutU4 uvrA6 and mutU4 recA, B, or C double mutants had mutation rates similar to that of a mutU4 strain. Two UV-sensitive mutators, mut-9 and mut-10, isolated by Liberfarb and Bryson in E. coli B/UV, were found to be co-transducible with ilv in the same general region as mutU4.

Excision repair characteristics of recB - res - and uvrC - strains of Escherichia coli

An Escherichia coli strain carrying the recB21 and res-1 mutations showed an abnormally low level of colony-forming ability although it grew essentially normally in liquid medium. The recB21 res-1 strain showed little, if any, of the ultraviolet (UV)-induced deoxyribonucleic acid (DNA) breakdown characteristic of the res-1 mutant. Nevertheless, the double mutant was far more sensitive to UV than either the res-1 or the recB21 strain. When compared with a wild-type strain, the rate of release of dimers from UV-irradiated DNA was very slow in the recB21 res-1, but normal in the res-1 recB(+) or recB21 res(+) mutants. However, the ratio of dimer-to-thymine released into the acid-soluble fraction was three times higher than the wild type in recB21 res(+) and recB21 res-1 and only one-tenth as high as the wild type in res-1 rec(+). Alkaline sucrose gradient centrifugation revealed occurrence of single-strand incision of UV-irradiated DNA and the restitution of nicked DNA at a similar rate in the recB21 res-1 and recB21 res(+) strains. Mutants uvrC(-) showed increased amounts of nicks in their DNA with increasing incubation time after UV irradiation, although no detectable amounts of dimers were excised from UV-irradiated DNA. From these results, it is concluded that the increased sensitivity of the res-1 strain to UV light is due to a reduced ability to excise dimers from UV-irradiated DNA and that the high rate of UV-induced breakdown of DNA is not the primary cause. A possible role of uvrC gene in the excision repair is discussed.