Recovery of phage lambda from ultraviolet damage

E. coli K12 inf: a mutant deficient in prophage lambda induction and cell filamentation

The bacterial mutant inf-3 (lambda) is not inducible and does not form filaments following thymine starvation. Lysogenic induction is neither produced by ultraviolet light (UV) nor promoted by tif-1. This phenotype is due to a mutation infA3 located between 60 and 73 min on the E. coli K12 map. The inf mutant is resistant to X-ray and UV irradiation, in contrast to all other known non-inducible bacterial mutants. It is Rec+ and able to perform host cell reactivation as well as UV-reactivation of phage lambda. After exposure to UV light, its DNA is degraded more than that of the parent and the resumption of DNA synthesis is delayed by 30 min; nevertheless, the cell survival is analogous to that of the parent. The inf mutant is also resistant to thymine starvation, for at least 3 hours. Wild type phage lambda forms clear plaques on a lawn of non-lysogenic inf bacteria; a corresponding low level of lysogenization is found. The capacity of inf bacteria to reproduce phages lambda, T4 or T6 is impaired. No gross defect in DNA transcription has been detected. Nevertheless, this mutant might have a slight alteration in the transcription process or in any other process involved in gene expression. This alteration might affect the regulation of DNA replication and cell division as well as prophage lambda induction.

Para-aminobenzoic acid inhibits a set of SOS functions in Escherichia coli K12

PABA - Vitamin H1 of group B, has obtained increasing fundamental interest as a very potent natural antimutagen after a series of our publications since 1979. In the first set of our experiments, we studied PABA in the assays with the alkylating agent N-methyl-N-nitrosourea (MNU). Mutagenic efficiency of this agent was suppressed up to 10-fold when PABA was administered into Escherichia coli cells concurrently with the mutagen or prior to the mutagenic treatment. NMR spectrometric and UV-spectrophotometric measurements did not reveal an interaction between the direct acting MNU and PABA, typical for some N-nitroso compounds and phenolics. PABA suppressed the error-prone DNA repair pathway induced by UV-irradiation. PABA decreased MNU-induced phage lambda lysogenic induction more than two orders of magnitude. PABA inhibited the thermal shift up to 400-fold in phage lambda from the permissive to non-permissive temperature in E. coli mutant tif-1 and decreased about two-fold W-reactivation of UV-damaged phage lambda. Chloramphenicol treatment of the cells just after the mutagenic treatment prevented the occurrence of PABA specific activity. The results suggest that PABA affects the SOS DNA repair pathway and the mutagenic response of E. coli. PABA appears to be an effective bioantimutagen reducing mutagenesis by modulating the error-prone DNA repair (SOS) response.

Inducible reactivation of UV-irradiated cholera phage e5 in Vibrio cholerae MAK757

The survival of UV-irradiated cholera phage e5 was found to increase when the host cells, Vibrio cholerae MAK757, were exposed to a low dose of UV irradiation before phage infection (Weigle reactivation), indicating the existence of a UV-inducible DNA repair pathway (SOS repair) in V. cholerae MAK757. The induction signal generated by UV irradiation was transient in nature and lasted about 20-30 min at 37 degrees C. Maximal Weigle reactivation of the phage was obtained when the host cells were irradiated with a UV dose of 16 J/m2. V. cholerae MAK757 was also found to possess efficient photoreactivation and host cell reactivation of UV-damaged DNA in phage e5.

Partial complementation of the UV sensitivity of E. coli and yeast excision repair mutants by the cloned denV gene of bacteriophage T4

The denV gene of bacteriophage T4 was reconstituted from two overlapping DNA fragments cloned in M13 vectors. The coding region of the intact gene was tailored into a series of plasmid vectors containing different promoters suitable for expression of the gene in E. coli and in yeast. Induction of the TAC promoter with IPTG resulted in overexpression of the gene, which was lethal to E. coli. Expression of the TACdenV gene in the absence of IPTG, or the use of the yeast GAL1 or ADH promoters resulted in partial complementation of the UV sensitivity of uvrA, uvrB, uvrC and recA mutants of E. coli and rad1, rad2, rad3, rad4 and rad10 mutants of S. cerevisiae. The extent of denV-mediated reactivation of excision-defective mutants was approximately equal to that of photoreactivation of such strains. Excision proficient E. coli cells transformed with a plasmid containing the denV gene were slightly more resistant to ultraviolet (UV) radiation than control cells without the denV gene. On the other hand, excision proficient yeast cells were slightly more sensitive to killing by UV radiation following transformation with a plasmid containing the denV gene. This effect was more pronounced in yeast mutants of the RAD52 epistasis group.

Prophage induction and filamentation in Bacillus thuringiensis caused by the genotoxic mycotoxin aflatoxin B1

Cultures of the lysogenic strain of Bacillus thuringiensis var. tolworthi were made in the presence of various drugs. The determination of bacterial size and plaque forming units (by using an indicator strain of B. thuringiensis var. galleriae) as well as colony forming units were then performed. Treatment of lysogenic cells by aflatoxin B1: provokes the formation of elongated cells (filamentation); induces a pathway that leads to the induction of prophage. Results of the present study indicated that filament formation and bacteriophage induction are two commonplace effects that occur in virtually every member of this cellular population exposed to low doses of certain drugs such as aflatoxin B1 (10 micrograms/ml); all of which have in common the ability to produce damaging changes in DNA. The following findings support the hypothesis that error-prone repair mechanisms seem to be present in B. thuringiensis as in Escherichia coli.

Weigle reactivation of diploid M13 phage

The limited ability of ultraviolet (UV)-irradiated E. coli cells to W-reactivate UV-irradiated, single-stranded DNA phages fd and M13 was investigated. The kinetics of induction for W-reactivation of UV-irradiated fd phage are different from that for other SOS functions. W-reactivation of UV-irradiated M13 phage was studied using phage particles that contain at least two single-stranded DNA genomes. No effect on the extent of W-reactivation of diploid phage was observed, compared to that of normal haploid phage, indicating that the mechanism of W-reactivation of single-stranded DNA phages does not involve recombination between partially replicated genomes.

Long repair replication patches are produced by the short-patch pathway in a uvrD252 (recL152) mutant of Escherichia coli K-12

The uvrD252 mutation leads to increased UV sensitivity, diminished dimer excision and host cell reactivation capacity, and an increase in the average patch size after repair replication. A recA56 uvrD252 double mutant was far more resistant to UV than was a recA56 uvrB5 double mutant. Its host cell reactivation capacity was identical to that of uvrD252 single mutant and was far greater than that of the uvrB5 single mutant. The strain showed no Weigle reactivation. From these results, we concluded that the double mutant has no inducible DNA repair (including long-patch excision repair) but retains dimer excision capabilities comparable to the uvrD252 single mutant. It appears, therefore, that the long patches detected in the uvrD mutant were not identical to the recA-dependent patches seen in wild-type cells.

Inducible reactivation of bacteriophage T7 damaged by methyl methanesulfonate or UV light

We examined the effects of host mutations affecting "SOS"-mediated UV light reactivation on the survival of bacteriophage T7 damaged by UV light or methyl methanesulfonate (MMS). Survival of T7 alkylated with MMS was not affected by the presence of plasmid pKM101 or by a umuC mutation in the host. The survival of UV light-irradiated T7 was similar in umuC+ and umuC strains but was slightly enhanced by the presence of pKM101. When phage survival was determined on host cells preirradiated with a single inducing dose of UV light, these same strains permitted higher survival than that seen with noninduced cells for both UV light- and MMS-damaged phage. The extent of T7 reactivation was approximately proportional to the UV light inducing dose inflicted upon each bacterial strain and was dependent upon phage DNA damage. Enhanced survival of T7 after exposure to UV light or MMS was also observed after thermal induction of a dnaB mutant. Thus, lethal lesions introduced by UV light or MMS are apparently repaired more efficiently when host cells are induced for the SOS cascade, and this inducible reactivation of T7 is umuC+ independent.

U.V. enhanced reactivation of U.V.-and gamma-irradiated adenovirus in normal human fibroblasts

An enhanced reactivation (UVER) of U.V.-irradiated as well as of gamma-irradiated human adenovirus type 2 (Ad 2) was detected following infection of normal human fibroblasts which had been pre-irradiated with U.V. light. U.V.-irradiated or non-irradiated fibroblasts were infected with either non-irradiated or irradiated Ad 2, and at 48 hours after infection cells were examined for the presence of viral structural antigens (Vag) using immunofluorescent staining. Results obtained using 5 different normal fibroblast strains showed that irradiation of host monolayers with 10J/m2 immediately prior to infection gave a U.V. enhanced reactivation (UVER) factor +/- standard error equal to 3 . 1 +/- 1 . 2 for virus U.V.-irradiated with 1 . 2 x 10(3) J/m2, and 2 . 1 +/- 0 . 5 for virus gamma-irradiated with 2 x 10(4) Gy. For a fixed survival of about 5 . 9 x 10(-2) for irradiated virus, the efficiency of UVER for gamma-irradiated virus was about 0 . 18, slightly less than the value of about 0 . 24 obtained for U.V.-irradiated virus. The results of time course experiments indicated that while U.V.-irradiation of normal host monolayers prior to infection gave rise to an increased rate of Vag formation for infection by unirradiated Ad 2, U.V.-irradiation of the cells increased the proportion of cells able to repair U.V.-damaged virus as well as allowing an earlier onset and/or increased rate of synthesis of Vag from a U.V.-damaged template. Similar experiments involving gamma-ray enhanced reactivation (gamma-RER) of irradiated Ad 2 indicated that gamma-RER and UVER may operate, in part at least, by different mechanisms in normal human cells.

Resident enhanced repair: novel repair process action on plasmid DNA transformed into Escherichia coli K-12

The survival of UV-irradiated DNA of plasmid NTP16 was monitored after its transformation into recipient cells containing an essentially homologous undamaged plasmid, pLV9. The presence of pLV9 resulted in a substantial increase in the fraction of damaged NTP16 molecules which survived in the recipient cells. This enhanced survival requires the host uvrA+ and uvrB+ gene products, but not the host recA+ gene product. The requirement for both homologous DNA and the uvrA+ and uvrB+ gene products suggests that a novel repair process may act on plasmid DNA. Possible mechanisms for this process are considered.

Weigle reactivation of the single-stranded DNA phage f1

The survival of ultraviolet light (UV) damaged single-stranded DNA bacteriophage f1 is increased when the Escherichia coli host is irradiated with UV prior to infection. This repair, called Weigle reactivation, is multiplicity independent and is absent in recA and in lexA mutants. The function of the recA-lexA repair system needed is repair and not recombination, as demonstrated by the absence of Weigle reactivation in mutants that are recombination proficient but defective in repair of double-stranded DNA. Weigle reactivation of f1 requires high levels of the recA protein, and in addition activation of recA or another protein. This activation can be produced by UV irradiation, or by the tif-1 allele of recA together with the spr allele of lexA. Mutagenesis of f1 has the same requirements as W-reactivation, and in addition requires UV irradiation of the phage.

W-reactivation of phage lambda in X-irradiated mutants of Escherichia coli K-12

The survival of UV irradiated phage lambda was increased on X-irradiated E. coli K-12 host cells over that on unirradiated cells. The frequency of c mutants among the surviving phages was to a similar extent increased by the X-ray exposure of the host cells as by UV light. This W-reactivation of phage lambda occurred in uvrA, polA, and recB mutants besides the wild type at about equal X-ray doses, however, at a reduced reactivation efficiency compared with the wild type. W-reactivation was undetectable in recA mutants. While maximal UV induced W-reactivation occurred 30 min after irradiation, the maximal X-ray induced reactivation was found immediately after irradiation. Chloramphenicol (100 micrograms/ml) and nitrofurantoin (50 micrograms/ml) inhibited W-reactivation of phage lambda if added before irradiation of the host cells, indicating the necessity of protein synthesis for W-reactivation.

Survival and mutagenesis in UV-irradiated phage: multi-hit kinetics of mutation induction and lack of indirect induction by infection with UV-irradiated phage of error-prone repair

The paper is concerned with the question of whether WEIGLE-reactivation (WR) and WEIGLE-mutagenesis (WM) can be indirectly induced by infection with UV-irradiated phage. Experiments neither with phage lambda of Escherichia coli nor with phage chi of Serratia marcescens show such induction-In this respects phage DNA differs from F'-DNA or Hfr-DNA; possible explanations are discussed. In both systems clear phage mutations can also be induced by UV without irradiation of the host cells; they appear, in unirradiated and irradiated host cells, with an increase of frequency which is greater than proportional to the UV dose. It is concluded that mutation induction of phage in the unirradiated host cells is due to a low level constitutive mutagenic repair; this could either be due to "spontaneous" induction of the mutagenic SOS-function or it could be a mechanism different from this one. Host irradiation would give rise to additional activity by the induced SOS-function leading to WR and WM. It is further concluded that deviation of the induction kinetics from a linear dose-dependence is not due to the necessary induction of SOS-functions.

Inactivation of prophage in ultraviolet-irradiated Escherichia coli: dependence on recA gene activity

The fate of the prophage part of the lysogenic chromosome was followed in the course of post-ultraviolet incubation. For this purpose, lambda cI857 ind prophage, which can be induced by heat but not by ultraviolet light, was used. The prophage, intially more resistant than its repair-proficient host cell, was rapidly inactivated. This inactivation was not caused by the impaired capacity of irradiated cells to support growth of the phage. Over the entire dose range tested, little, if any, sensitivity difference between the host and the prophage was found at the end of cell division delay. Rapid inactivation of the prophage was also observed in uvr cells after small doses of ultraviolet light. The same small doses did not cause inactivation in lysogens carrying a mutation in the gene recA. This suggests that the functional gene recA is required for inactivation of the prophage part of the lysogenic chromosome.

W reactivation is inefficient in repair of the bacterial chromosome

UV-inducible "SOS" processes associated with W reactivation of phage lambda were studied for their effect on repair of lambda prophage integrated in the bacterial chromosome. For this purpose, lambda c1857 ind red-lysogens were used. These lysogens, although non-inducible by UV light, can be induced by raising the temperature from 30 degrees to 42 degrees. If the W reactivation processes are involved in repair of the bacterial DNA, when the lysogens are incubated at 30 degrees after UV exposure W reactivation should be fully expressed and should also exert an effect on the bacterial chromosome and the prophage inside it. When heat-induction is delayed until the time at which W reactivation reaches its maximum, a considerable increase in phage survival might then be expected. The results presented in this report show, however, that the delayed induction had only a small effect on the survival of prophage in the wild-type strain (possibly attributable to excision repair) and no detectable effect on prophage in a uvrA strain. From these results we conclude that W reactivation is largely irrelevant to the repair of UV-damaged bacterial DNA.

Mutagenesis and repair deficiencies of Escherichia coli umuC mutants are suppressed by the plasmid pKM101

The presence of the drug resistance plasmid pKM101 restored the ability of Escherichia coli umuC mutant strains to be mutated by methyl methanesulfonate. Inducible (Weigle) reactivation of ultraviolet-irradiated bacteriophage lambda was not observed in uvrA6 umuC mutant strains lacking pKM101 but was observed if the plasmid was present in the strains. In a uvrA+ umuC36 strain pKM101 increased the efficiency of the Weigle reactivation process. Plasmid-mediated UV-resistance and plasmid-mediated phage reactivation were observed in umuC(pKM101) strains both in uvrA+ and uvrA6 backgrounds. No restoration of methyl methanesulfonate mutability by pKM101 was observed in umuC36 recA56 strains. pKM101 mutants unable to enhance mutagenesis in umuC+ backgrounds also had no effect on methyl methanesulfonate mutagenesis in umuC mutant strains. Neither a umuC mutation nor the presence of pKM101 affected the UV induction of protein X, the recA protein. Hypotheses relating the mode of action of pKM101 to the process of mutagenesis and inducible phage reactivation are discussed.

W-reactivation of phage lambda in recF, recL, uvrA, and uvrB mutants of E. coli K-12

W-reactivation is reduced by recF143 and recF144 mutations and is undetectable if a second mutation at either the uvrA or uvrB locus is combined with recF143. The uvrA and uvrB mutations alone block W-reactivation partially. A recL152 mutation also partially blocks W-reactivation by itself. In combination with a uvrB5 mutation, recL125 blocks W-reactivation completely but in combination with recF143, significant residual W-reactivation ability remains. We suggest that the phenomenon of W-reactivation is the result of at least two modes or pathways. The observation that recF143 uvrB5 and recF143 uvrA6 strains permit normal levels of mutagenesis (Kato et al., 1977) but completely block all W-reactivation leads us to suggest further that the mechanism(s) of W-reactivation is at least partly different from that of UV mutagenesis.

Inducible reactivation and mutagenesis of UV-irradiated bacteriophage P22 in Salmonella typhimurium LT2 containing the plasmid pKM101

The inducible (Weigle) reactivation of UV-irradiated bacteriophage P22 has been examined on strains of Salmonella typhimurium with and without the mutagenesis-enhancing plasmid pKM101. A large inducible reactivation was observed in the plasmid-containing strain, but only a small response was observed in the strain lacking the plasmid. An increased frequency of clear-plaque mutants was detected among the survivors. The efficiencies of the plasmid-mediated and cellular repair processes have been determined. The kinetics of induction of the phage reactivation have been investigated. The relationship of the observed results to the inducible reactivation of UV-irradiated lambda in Escherichia coli and to error-prone repair is discussed.

Induction of lambda prophage and of mutations to streptomycin resistance in separate small fractions of a lysogenic derivative of Escherichia coli B/r by very low doses of ultraviolet light

The number of induced mutations to streptomycin resistance is compared at doses of ultraviolet (UV) light between 0.2 and 6.4 J/m2 in a Uvr- (excision-deficient) derivative of E. coli B/r, strain WU, and in its lambda lysogen, strain WU(lambda). At UV doses up to about 1 J/m2, which converts about 5% of the lysogenic population into enfective centers, no difference is observed in the number of mutations to streptomycin resistance produced by the two strains. It is concluded that the capacity to produce UV-induced mutations is not coupled with lysis due to the induction of lambda prophage at low doses of UV radiation. At UV doses above 1 J/m2, the number of mutatants detected in the lysogenic strain decreases appreciably compared to the number detected in the nonlysogen, and is only about 10% as high at UV doses of 3 J/m2 and higher, doses which cause maximal induction of prophage. The results are compatible with the operation of a common "all-or-none" induction signal resulting in expression of UV-inducible functions at high UV doses, but not at low doses.

Characterization of lexB mutations in Escherichia coli K-12

Two mutations have been located at the recA locus and phenotypically characterized along with a third one, previously called rec-34. The three mutants behaved similarly to lexA mutants. They were sensitive to ultraviolet (UV) light and X rays, and lambdaFec- phages were able to plate on them. The three mutations were called lexB because they could be distinguished from recA mutations by the last property. lexB mutants were less sensitive to UV and X irradiations than were recA mutants and were, to various degrees, recombination proficient. UV light failed to induce prophage lambda in all three lexB lysogens. In contrast, thymine starvation induced lexB31 and lexB34 lysogens. In lexB34 mutants, but not in lexB30 and lexB31 mutants, UV reactivation occurred at a low level. In Escherichia coli K-12, the recA gene has basic functions in the repair of deoxyribonucleic acid lesions, deoxyribonucleic acid recombination, and prophage induction. The three lexB mutations alter unequally and independently the three functions. This suggests that the recA and lexB mutations affect the same gene.

Growth and reactivation of single stranded DNA phage phiX174 in E. coli undergoing "thymineless death"

The thymine requirement of the E. coli strain HF 4704 (uvr A-, rec A+) is thermosensitive i.e. these cells require for their growth 2 microng thymine per ml at 37 degrees C but not at 30 degrees C. Such cells when starved for thymine for 3 h at 37 degrees C are capable of sustaining growth of single stranded DNA phage phiX174 without any diminution of burst size under nonpermissive conditions. Thymine starved HF 4704 cells also reactivate UV-irradiated phiX174 by about 3fold. To test if the thymine necessary for phage growth under "thymineless" conditions was supplied by host DNA degradation products, the transfer of 32P label from the host DNA to mature progeny phages was measured by means of sucrose density gradient analysis. It was found that only about 0.7% of 32P of the host DNA was transferred to the progeny phages growing in normal cells whereas the corresponding value was 7.8% in the case of thymine starved cells.

Host cell and ultraviolet reactivation of ultraviolet-irradiated Mycoplasmaviruses

The mycoplasma Acholeplasma laidlawii was shown to have mechanisms for both host cell and ultraviolet (UV) reactivation of UV-irradiated mycoplasmaviruses. Host cell reactivation was examined by comparing the survival abilities of UV-irradiated double-stranded deoxyribonucleic acid mycoplasmavirus plated on both untreated and on acriflavine-treated cells. Acriflavine treatment inhibited cell exision repair. Decreased survival on the acriflavine-treated cells demonstrated host cell reactivation. UV reactivation was studied by comparing the survival of UV-irradiated virus plated on untreated cells with its survival on cells that received a small UV dose before plating. The UV-irradiated cells gave increased virus survival, showing UV reactivation. Similar experiments with a single-stranded deoxyribonucleic acid mycoplasmavirus showed that this virus could be UV reactivated, but not host cell reactivated.

Ultraviolet mutagenesis and inducible DNA repair in Escherichia coli

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Inducible, error-free DNA Repair in tsl recA mutants of E. coli

Host of cell reactivation and UV reactivation and mutagenesis of UV-irradiated phage mu were measured in tsl recAplus and tsl recA host mutants. Host cell reactivation was slightly more efficient in the tsl recA strain. Phage was UV-reactivated in the tsl recA strain with about one-half the efficiency of that in the wild type strain, but there was no corresponding mutagenesis of phage. UV-reactivation was also slightly lower and mutagenesis several-fold lower than normal in the tsl recAplus strain. To account for these observations, we propose that there is an inducible, error-free pathway of DNA repair in E. coli that competes with error-prone repair for repair of phage lesions.