Excision Repair-deficient Strains Research Articles

Effect of UV absorbers on UV-induced mutagenesis in E. coli B/r.

Effects of cosmetic UV absorbers on UV-induced mutagenesis in E. coli B/r strains were studied. Among 8 substances tested, cinoxate (2-ethoxyethyl p-methoxycinnamate) enhanced UV (254 nm)-induced mutation at non-lethal toxic doses. This adverse effect was also observed when the mid and near-UV (295 nm-400 nm) irradiated cells of WP2 were used. This effect, however, was not observed in WP2s uvr A, a DNA excision repair deficient strain of E. coli B/r. It is thus assumed that cinoxate inhibited DNA excision repair system and consequently increased UV-induced mutation.

Bio-antimutagenic effects of tannic acid on UV and chemically induced mutagenesis in Escherichia coli B/r

Tannic acid suppressed the mutagenesis in E. coli B/r WP2 trp − induced by UV or 4-nitroquinoline 1-oxide (4NQO), but not that induced by γ-rays or N-methyl- N′-nitro- N-nitrosoguanidine (MNNG). The depression of mutations induced by UV was most remarkable in the DNA-repair-proficient strain (WP2). Tannic acid, however, showed no bio-antimutagenic effect in the excision repair-deficient strain (WP2 s uvrA − or ZA159 uvrB −) under the test conditions where no cellular toxicity was observed. The effect ceased within 30 min after UV irradiation. The inhibition of the expression of Trp + phenotype and the delay of the first cell division after UV irradiation were not observed in the presence of tannic acid. From these results we conclude that tannic acid may enhance the excision-repair system probably by activating the repair enzymes or by interacting with DNA.

LAW OF RECIPROCITY IN UV ERYTHEMA AND CELL KILLING

ABSTRACTThe dose rate effect of ultraviolet light (UV) was investigated from a view point of the law of reciprocity both in vivo and in vitro. The reciprocity in UV erythema reaction was examined in seven excision repair deficient xeroderma pigmentosum (XP) patients with monochromatic UV at wavelengths of 255 nm and 290 nm using a 1% neutral filter (NF) to reduce UV intensity to 1/100. For the in vitro study, the reciprocity in UV cell killing was examined in four normal and three excision repair deficient XP fibroblast strains using varied intensities to 1/100 at 254 nm.As in the results obtained by Satoh et al. in normal subjects, the law of reciprocity did not hold for erythema reaction in XP patients at 255 nm when the dose rate was changed a hundred fold. In the XP patients, the minimal erythema dose (MED) required by 1/100 intensity was on the average 1.57 times higher for 255 nm and 1.12 times higher for 290 nm as compared with MED without NF. On the other hand, the law of reciprocity was found to hold for cell killing in both normal and XP cells by 254 nm UV at the intensity range of 1:100.

Evidence for Two Modes of DNA Degradation in Escherichia coli Following Ultraviolet Irradiation

UV-induced DNA degradation is found in wild-type E. coli strains and is greatly reduced by photoreactivation. UV-induced DNA degradation is not found in an excision repair-deficient strain (uvr A) unless incubated post-UV in the presence of chloramphenicol. Chloramphenicol-enhancible degradation is significant and is not reduced by photoreactivation. Greater DNA degradation is found in cells irradiated frozen at -79/sup 0/C than in cells irradiated at ambient temperature (21/sup 0/C). When the cells are irradiated at -79/sup 0/C the amount of degradation is very slightly decreased by photoreactivation. Chloramphenicol-enhancible DNA degradation does not occur in a lexA strain. These data suggest two modes of UV-induced DNA degradation, one responding to pyrimidine dimers and one responding to lesions other than dimers, with chloramphenicol-enhancible degradation corresponding to the second mode.

Expression of an excision repair gene in transformation of Bacillus subtilis

DNA of Bacillus subtilis proficient in excision repair (hcr+) was introduced into Angiografinpurified competent cells of an excision repair-deficient strains UVS-1 (hcr-1). The hcr+ gene was found to affect the UV-survival curve of the cells, giving rise to a UV-resistant component. However, a considerable number of colonies of the UV-resistant component consisted of cells that were not transformed to hcr+ as judged by their sensitivity to mitomycin C (MC), UV, and by their ability to reactivate UV-irradiated M2 phages. This suggests that the hcr gene may be expressed without integration. The recA function of B. subtilis was necessary for expression of UV resistance to occur. When DNA-treated cells were selected for met+ recombinants, the UV-resistant component was again found on the UV-survival curve and about half of the colonies of the UV-resistant component consisted of Hcr- cells. This result was explained by an integration-segregation model for hcr+ and met+ genes. The effect of the hcr+ gene was seen even when DNA was added after cells were irradiated with UV, although this effect was gradually diminished by delaying the time of DNA addition. A complementation effect was found between two excision repair mutations residing in two distant loci, using hcr-114 DNA as a donor and hcr-1 cells as a recipient.

Vinyl chloride mutagenicity via the metabolites chlorooxirane and chloroacetaldehyde monomer hydrate

Mutagenicity tester strains of Bacillus and Salmonella were used to assay vinyl chloride in nutrient broth at a practical concentration level. Also screened without exogenous activation were seven potential metabolites of vinyl chloride in their pure forms as well as the related epichlorohydrin. Chlorooxirane, chloroacetaldehyde, chloroacetaldehyde monomer hydrate, chloroacetaldehyde dimer hydrate, chloroacetaldehyde trimer, and epichlorohydrin produced significant mutagenic activity in Salmonella typhimurium strains sensitive to basepair mutation. A recombination repair deficient strain of Bacillus subtilis was inhibited in growth by these compounds, whereas excision repair deficient and wild type strains of Bacillus subtilis were relatively unaffected. On the basis of these assays a working hypothesis for the vinyl chloride carcinogenesis mechanism is proposed which involves chlorooxirane and chloroacetaldehyde monomer hydrate as the ultimate carcinogenic metabolites of vinyl chloride.

Colony-forming ability of ultraviolet-irradiated xeroderma pigmentosum fibroblasts from different DNA repair complementation groups

Patients with xeroderma pigmentosum develop severe sunlight-induced damage, including malignant neoplasms, on sun-exposed skin. Some patients also have neurological abnormalities. Xeroderma pigmentosum cells are known to have impaired ability to repair ultraviolet light- or chemical mutagen-induced damage to their DNA, and cell-fusion studies have shown five complementation groups among the DNA excision repair-deficient strains. All xeroderma pigmentosum fibroblast strains we tested had lower colony-forming abilities after ultraviolet irradiation than normal strains. Furthermore, we have found that strains from different complementation groups can have different post-ultraviolet colony-forming abilities and that strains from patients with neurological abnormalities are the most sensitive to ultraviolet light. These results suggest that extremely ineffective repair of damaged DNA in central nervous system neurons may be the cause of the neurological abnormalities.

Effects of sodium arsenite on the survival of UV-irradiated Escherichia coli: Inhibition of a recA-dependent function

Epidemiological studies and clinical observations suggesting potential hazards of arsenic compounds in increasing the incidence of cancer have been in complete contradiction with experimental findings in animals. Because of the predominance of skin cancers in the epidemiological reports, we decided to investigate the possibility that arsenic compounds might interfere with DNA repair. Using Escherichia coli as a test system, we show that this is indeed the case. Sodium arsenite, at concentrations of 0.1 m M and higher, decreases the survival of ultraviolet-irradiated E. coli WP2, a strain which possesses the full complement of repair genes. The effect of the arsenite increases with increasing ultraviolet dose. Similar results were obtained with the excision repair deficient strains WWP2 ( uvrA ) and WP6 ( polA ). Sodium arsenite had no effect on the survival of a rec A mutant, WPio. Survival of ultraviolet-irradiated WP5 ( exr A ) was enhanced by sodium ardenite, the effect being greatest at low ultraviolet doses. It is postulated that arsenite inhibits a rec A -dependent step in DNA repair. To account for the increased survival of the exr A mutant, we suggest that in the absence of the exr + gene, the arsenite-sensitive rec A -dependent function is deleterious. The ability of arsenite to inhibit DNA repair may account for the clinical and epidemiological reports linking arsenicals with an increased incidence of cancer.

Effects of sodium arsenite on the survival of UV-irradiated Escherichia Coli: INHIBITION OF A rec A-Dependent function

Epidemiological studies and clinical observation suggesting potential hazards of arsenic compounds in increasing the incidence of cancer have been in complete contradiction with experimental findings in animals. Because of the predominance of skin cancers in the epidemiological reports, we decided to investigate the possibility that arsenic compounds might interfere with DNA repair. Using Escherichia coli as a test system, we show that this is indeed the case. Sodium arsenite, at concentrations of 0.1 mM and higher, decreases the survival of ultraviolet-irradiated E. coli WP2, a strain which possesses the full complement of repair genes. The effect of the arsenite increases with increasing ultraviolet dose. Similar results were obtained with the excision repair deficient strains WWP2 (uvrA) and WP6 (polA). Sodium arsenite had no effect on the survival of a recA mutant, WP10. Survival of ultraviolet-irradiated WP5 (exrA) was enhanced by sodium ardenite, the effect being greatest at low ultraviolet doses. It is postulated that arsenite inhibits a recA-dependent step in DNA repair. To account for the increased survival of the exrA mutant, we suggest that in the absence of the exr+ gene, the arsenite-sensitive recA-dependent function is deleterious. The ability of arsenite to inhibit DNA repair may account for the clinical and epidemiological reports linking arsenicals with an increased incidence of cancer.

Effects of sodium arsenite on the survival of UV-irradiated Escherichia coli: Inhibition of A recA-dependent function

Epidemiological studies and clinical observations suggesting potential hazards of arsenic compounds in increasing the incidence of cancer have been in complete contradiction with experimental findings in animals. Because of the predominance of skin cancers in the epidemiological reports, we decided to investigate the possibility that arsenic compounds might interfere with DNA repair. Using Escherichia coli as a test system, we show that this is indeed the case. Sodium arsenite, at concentrations of 0.1 m M and higher, decreases the survival of ultraviolet-irradiated E. coli WP2, a strain which possesses the full complement of repair genes. The effect of the arsenite increases with increasing ultraviolet dose. Similar results were obtained with the excision repair deficient strains WWP2 ( uvrA ) and WP6 ( polA ). Sodium arsenite had no effect on the survival of a rec A mutant, WPio. Survival of ultraviolet-irradiated WP5 ( exr A ) was enhanced by sodium ardenite, the effect being greatest at low ultraviolet doses. It is postulated that arsenite inhibits a rec A -dependent step in DNA repair. To account for the increased survival of the exr A mutant, we suggest that in the absence of the exr + gene, the arsenite-sensitive rec A -dependent function is deleterious. The ability of arsenite to inhibit DNA repair may account for the clinical and epidemiological reports linking arsenicals with an increased incidence of cancer.

Oxygen dependence and repair of lethal effects of near ultraviolet and visible light.

Abstract— –Lethality in a repairable strain (WP2) and an excision repair deficient strain (WP2hcr) of Escherichia coli was studied at wavelengths of 254, 313, 365, and 390–750 nm. Survival curves were empirically fitted to the expression S= 1 ‐ (1‐e‐kl)“, where S is the fraction surviving, D is the incident dose in ergs mm‐2, k is the inactivation constant in units of (erg mm‐2)‐1 and n is the ‘shoulder constant’. The repairable sector (k(hcr‐)–k(hcr‐)lk(hcr‐), a conservative estimate of the repair capability of E. coli WP2, was 0.91 at 254 nm, 0.92 at 313 nm, 0.60 at 365 nm, and 0.13 at 390–750 nm. Although there was no oxygen enhancement of inactivation at 254 nm and 313 nm, a strong enhancement was identified at 365 nm and 390–750 nm. These results suggest that oxygen‐dependent damage induced by near u.v. (365 nm) can be partially repaired by the excision‐repair system in E. coli.