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Further phenotypic characterization of pso mutants of Saccharomyces cerevisiae with respect to DNA repair and response to oxidative stress

Cristina Pungartnik1, Jaqueline Picada1, Martin Brendel2 and João A.P. Henriques1
1Departamento de Biofísica/Centro de Biotecnologia, UFRGS,Av.Bento Gonçalves, 9500, 91507-970 Porto Alegre, RS, Brazil
2Institut für Mikrobiologie der J.W. Goethe-Universität, Frankfurt am Main, Germany
Corresponding author: J.A.P. Henriques
E-mail: [email protected]
Genet. Mol. Res. 1 (1): 79-89 (2002)
Received March 7, 2002
Published March 26, 2002

ABSTRACT. The sensitivity responses of seven pso mutants of Saccharomyces cerevisiae towards the mutagens N-nitrosodiethylamine (NDEA), 1,2:7,8-diepoxyoctane (DEO), and 8-hydroxyquinoline (8HQ) further substantiated their allocation into two distinct groups: genes PSO1 (allelic to REV3), PSO2 (SNM1), PSO4 (PRP19), and PSO5 (RAD16) constitute one group in that they are involved in repair of damaged DNA or in RNA processing whereas genes PSO6 (ERG3) and PSO7 (COX11) are related to metabolic steps protecting from oxidative stress and thus form a second group, not responsible for DNA repair. PSO3 has not yet been molecularly characterized but its pleiotropic phenotype would allow its integration into either group. The first three PSO genes of the DNA repair group and PSO3, apart from being sensitive to photo-activated psoralens, have another common phenotype: they are also involved in error-prone DNA repair. While all mutants of the DNA repair group and pso3 were sensitive to DEO and NDEA the pso6 mutant revealed WT or near WT resistance to these mutagens. As expected, the repair-proficient pso7-1 and cox11-D mutant alleles conferred high sensitivity to NDEA, a chemical known to be metabolized via redox cycling that yields hydroxylamine radicals and reactive oxygen species. All pso mutants exhibited some sensitivity to 8HQ and again pso7-1 and cox11-D conferred the highest sensitivity to this drug. Double mutant snm1- cox11-D  exhibited additivity of 8HQ and NDEA sensitivities of the single mutants, indicating that two different repair/recovery systems are involved in survival. DEO sensitivity of the double mutant was equal or less than that of the single snm1-D  mutant. In order to determine if there was oxidative damage to nucleotide bases by these drugs we employed an established bacterial test with and without metabolic activation. After S9-mix biotransformation, NDEA and to a lesser extent 8HQ, lead to significantly higher mutagenesis in an Escherichia coli tester strain WP2-IC203 as compared to WP2, whereas DEO-induced mutagenicity remained unchanged.

Key words: DNA damage, Drug metabolism, Oxidative stress, DNA repair, Yeast, Escherichia coli mutagenesis

 

INTRODUCTION

The pso mutants of Saccharomyces cerevisiae were isolated due to their sensitivity to photoactivated psoralens (Henriques and Moustacchi, 1980; Henriques et al., 1989; Querol et al., 1994). With increasing phenotypic characterization a division of the hitherto known seven PSO genes into two groups, based on their involvement with DNA repair, was suggested (Henriques et al., 1997). While PSO1 (allelic to REV3), PSO2 (allelic to SNM1), PSO4 (allelic to PRP19), and PSO5 (allelic to RAD16) encode proteins with known or apparent functions in either error-prone or error-free DNA repair, the PSO6 (allelic to ERG3) and PSO7 genes (allelic to COX11) encode proteins apparently not involved in a DNA repair mechanism. Mutant alleles of the latter genes most probably confer sensitivity to certain mutagens as a result of loss from protection to reactive oxygen species (ROS) by low ergosterol in pso6/erg3 (Schmidt et al., 1999) or due to altered mutagen metabolism in pso7/cox11 (induced by an electron flow impairment; Pungartnik et al., 1999). PSO3 has not yet been molecularly characterized and, though it exhibits defects in error-prone repair (Cassier et al., 1980) and, therefore, should belong to the first group of repair-deficient pso mutants, it might as well be associated with PSO6 and PSO7, since the pso3-1 mutation, as all mutant alleles from the second group of repair-proficient pso mutants, confers sensitivity to oxidative stress-inducing treatments (Querol et al., 1994; Brendel et al., 1998; Schmidt et al., 1999; Pungartnik et al., 1999), as do all mutant alleles from the second group of repair-proficient pso mutants.

In the present study, we show some new phenotypes for the pso mutants in which we have determined their sensitivities to the three selected mutagens: N-nitrosodiethylamine (NDEA, which after hydroxyl radical formation decomposes to acetaldehyde and an alkylating agent; Bartsch et al., 1989); 1,2:7,8-diepoxyoctane (DEO, a cross-linking and deletogenic agent; Yunes et al., 1996; Picada et al., 1999), and 8-hydroxyquinoline (8HQ, which is only mutagenic after biotransformation/metabolic activation; Nagao et al., 1977). Furthermore, we have applied these chemicals to yeast double mutants containing one pso mutant allele from each group in order to assess whether an epistasis/synergism analysis (Brendel and Haynes, 1973; Brendel and Ruhland, 1984) might indicate possible interactions of the respective PSO gene-encoded proteins in protection from, or repair of, DNA damage induced by these agents in yeast. Finally we have indirectly verified the production of ROS in the course of NDEA and probably also 8HQ metabolic activation by showing their elevated mutagenicity in Escherichia coli tester strain WP2-IC203 that specifically indicates ROS-induced DNA lesions (Blanco et al., 1998).

MATERIAL AND METHODS

Strains and media

The yeast strains used are given in Table 1. Strains were usually grown and stored on YPD media. To ascertain their respiratory competence and for elimination of spontaneously accumulated petites all strains (except cox11 deletion mutants) were pre-grown on YP glycerol media (glucose replaced by 3% glycerol) before being grown in YPD. All media, general and genetical procedures were as described before (Ruhland et al., 1981a). E. coli strains WP2 uvrA/pKM101 (WP2) and WP2 uvrA oxyR/pKM101 (IC203) were obtained from M. Blanco, Instituto de Investigaciones Citológicas, Spain.

Treatment with chemicals

Yeast strains were grown in YPD under shaking at 30°C for 2 days (stationary phase). These cells were screened for their sensitivity in the center well test (Ruhland et al., 1981a). Having established the appropriate range of concentration for each mutagen, the sensitivities of WT, pso single and double mutants were determined as follows: a) NDEA was added to YPD agar plates to a final concentration of 40 and 80 mM and 5 ml drops of a 1:10 dilution series from undiluted culture (approximately 2 x 108 cells/ml) to dilution 10-5 (approximately 2 x 103 cells/ml) of up to 5 different strains were applied to the same plate. Incubation was for 2 to 3 days at 30°C. Strains from the tetrad analysis were treated with lower NDEA concentrations; b) Sensitivity to DEO and to 8HQ was routinely determined in liquid YPD media. Exposure concentrations in 1 ml samples were 10 and 20 mM (for DEO) and 20 and 40 mM (for 8HQ), and exposure time was 1 h at 30°C. Treated cells were diluted in distilled water as in (a) and 5 ml drops from each dilution were spotted onto YPD agar plates. In some instances DEO was applied to washed cells suspended in either phosphate buffer, pH 7.0, or distilled water for testing of a possible influence of medium components and pH on DEO reactivity.

Mutagenicity testing

E. coli strains WP2 and IC203 were exposed to the three chemicals that had been/had not been treated with S9-mix (Molecular Toxicology Inc.; MoltoxTM, prepared from livers of Sprague-Dawley rats pretreated with polychlorinated biphenyls (Aroclor 1254)). Testing for mutagenicity was as described by Blanco et al. (1998).

RESULTS AND DISCUSSION

The survival of haploid WT and pso mutant cells of yeast after exposure to the three chemicals is shown for some strains in Figure 1 and summarized for all pso mutants in Table 2. Exposure concentrations of the mutagens were such that the WT cells showed no killing at the highest exposure dose, whereas mutant cells normally exhibited a varying degree of sensitivity in survival. Two WT strains were used because the tested pso mutants were derived from either one of them (Table 2).

The chemical 8HQ is not genotoxic unless metabolically activated, e.g., by rodent liver or by S9-mix (Hollstein et al., 1978; Willems et al., 1992); mutagenic activity of 8HQ was correlated to the formation of water-soluble quinoline intermediate metabolites, which constitute epoxide derivatives that could form DNA adducts (Tada et al., 1980).

After 1-h exposure to 20 and 40 mM 8HQ the seven pso mutants display a wide spectrum of sensitivities to this pro-mutagen, whereas the two WT strains were completely resistant (Table 2). Interestingly, the pso7/cox11 mutation confers the highest 8HQ-sensitivity amongst all yeast strains tested, whereas all mutants from the DNA repair-deficient group, while also 8HQ-sensitive, were clearly much more resistant than the DNA repair-proficient pso7/cox11 mutant (Table 2). Mutant alleles pso2-1/snm1-D confer low 8HQ-sensitivity which is not surprising as this mutant is known to be specifically sensitive to interstrand cross-link (ICL) producing mutagens (Ruhland et al., 1981b) and the pso6/erg3 mutant allele does not confer any sensitivity at all and survives like a WT. The highly reactive diol epoxides that may emerge at some point of 8HQ biotransformation (Willems et al., 1992) and that can form DNA adducts may explain the sensitivity of group I pso mutants. On the other hand, the extreme sensitivity of DNA repair-proficient mutant pso7/cox11 suggests that 8HQ, very much like 4NQO, might be metabolized via a redox cycle induced by altered electron flow that would generate nitroquinoline radicals and consequently highly genotoxic ROS (Pungartnik et al., 1999).

Sensitivity to NDEA

NDEA is a potent carcinogen that turns mutagen in Salmonella typhimurium (TA98 and TA100) when activated by alcohol dehydrogenase (ADH) from yeast or horse liver. Nitrosamine compounds can easily be activated by redox cycling, producing nitrosamine-derivative radicals and ROS (Boveris, 1998); the latter may induce lipid peroxidation (LP) (Ahotupa et al., 1987; Kappus and Sies, 1981). All pso mutants, being proficient in at least 5 different ADHs (Wehner et al., 1993) showed higher-than-WT sensitivity to NDEA (Figure 1 and Table 2). Highest sensitivities were displayed by the group of repair-deficient mutants pso1, pso4, pso5, and pso3, whereas ICL-specific repair mutant pso2/snm1 (Ruhland et al., 1981b) had only intermediate NDEA-sensitivity. These responses clearly show that activated NDEA caused significant numbers of DNA lesions (few or none of the ICL type) throughout the yeast genome, the pso5/rad16 mutant’s (Paesi-Toresan et al., 1995) high sensitivity pointing to the importance of a functional Rad16p/Pso5p for excision repair in silent regions of the genome or in non-transcribed strands of DNA (Verhage et al., 1994).

As would be expected, the DNA repair-proficient pso6 and especially pso7 mutants (pso7-1 and cox11-D) were also NDEA-sensitive (Table 2). For the pso6/erg3 mutant this may be explained by its lower ergosterol content (Schmidt et al., 1999) that would offer less protection from NDEA-induced LP (which was shown to rapidly occur in rat liver after NDEA had been metabolized into a pro-oxidant state; Ahotupa et al., 1987). This is coupled with increased production of ROS, ultimately leading to a larger number of oxidative DNA lesions. NDEA metabolism may also be accelerated in pso7 by enhanced redox cycling due to altered electron flow (Pungartnik et al., 1999) leading to high levels of nitrosamine derivatives and ROS. Finally, the pso3 mutant is known to be sensitive to ROS (Brendel et al., 1998) and also has an impaired error-prone DNA repair (Henriques et al., 1997). Its high NDEA-sensitivity may, therefore, indicate that the Pso3p has a special role in repair of oxidative DNA damage, and that nonrepair of such lesions would result in lower-than-WT mutagenesis and higher-than-WT sensitivity

Sensitivity to DEO 

The carcinogenicity of epoxide compounds has been attributed to their covalent binding to DNA. While monoepoxides form only monoadducts, diepoxides can also form ICL. Depending on their chain length diepoxides may form DNA-ICL and show higher carcinogenicity and mutagenicity than their monoepoxide analogues (for a review, see Yunes et al., 1996; Vock et al., 1999). Sensitivity to the ICL forming and deletogenic (Picada et al., 1999) agent DEO of all 7 pso mutants is shown in Table 2. As with NDEA all mutants of the repair-deficient group (pso1, pso2, pso4, with exception of pso5) were highly sensitive to DEO, again demonstrating the importance of error-free and error-prone repair in removal of DNA lesions induced by the mono- and bifunctional action of DEO. The low DEO-sensitivity of pso5/rad16 indicates that there is either very low DNA damage (in number or in stability of DNA lesions) in silent and non-transcribed regions of the yeast genome (Verhage et al., 1994) or that the still existing residual excision repair in a rad16 mutant (Reed et al., 1998) suffices to remove most of DEO-induced DNA lesions. Indeed a rad16-1 mutant had no repair of 8-methoxypsoralen (8-MOP + UVA)-induced ICL in the silent mating type locus HMLa whereas incision near ICL in the transcriptionally active MATa locus was normal (Meniel et al., 1995). Alternatively, ICL repair in transcribed regions of the genome might be more severely inhibited or lead to lethal DNA processing in the other repair-deficient pso mutants and hence enhance their sensitivity over that of rad16/pso5.

The increased sensitivity of pso7/cox11 mutants to DEO, however, is surprising since these mutants have WT-like capacity for DNA repair (Henriques et al., 1997) and since DEO has not yet been shown to be involved in, or capable of, inducing ROS (see below). We might, therefore, speculate that DEO metabolism in the pso7/cox11 mutant could lead to altered derivatives with significantly higher DNA-damaging potential while the WT-like resistance of the pso6 mutant indicates that lack of ergosterol does not lead to a larger number of DNA lesions. Finally, the sensitivity of pso3-1 to DEO was expected, as this mutant is known to be sensitive to 8-MOP + UVA treatment that leads to DNA-ICL (Henriques and Moustacchi, 1980)

Sensitivities to DEO, NDEA and 8HQ of snm1-D cox11-D double mutants 

A synergistic or epistatic interaction of two mutant alleles which each alone confer a similar phenotype, in our case sensitivity to a given mutagen, could give a first indication whether the two mutant alleles affect interrelated metabolic steps (epistasis), competitive (synergism) or unrelated (additivity) metabolic pathways of damage prevention/repair (Brendel and Haynes, 1973). Sensitivity to the three mutagens of haploid strains containing all possible allele combinations of PSO2 and PSO7 (WT, single and double mutants represented by the snm-D and cox11-D mutant alleles) is shown in Table 3. In addition to DEO three typical DNA cross-linking agents or treatments, nitrogen mustard (HN2), triaziquone (Ruhland et al., 1981b) and

photoactivated 8-MOP + UVA (Bankmann and Brendel, 1989) were used to verify the pso2/snm1 mutant’s sensitivity to DNA-ICL (Table 3). The four haploid yeast strains tested are from one tetratype tetrad derived from one ascus of the sporulated diploid MG5503 that was generated by the cross of the haploid cox11 and snm1 mutants (Table 1).

Analyses of the 8HQ-sensitivities of the four allele combinations revealed a non-epistatic (additive or synergistic) interaction of the two mutant alleles at 20 mM but not at 40 mM exposure concentration (first two columns in Table 3). This points to unrelated metabolic activities of the two related proteins in protection from the toxic/genotoxic effects of biotransformed 8HQ in yeast.

The sensitivity to NDEA of both pso2-1/snm1-D and pso7-1/cox11-D mutants, the former representing impaired DNA repair and the latter with a defect in mitochondrial function, enabled us to test our hypothesis that these two PSO genes do not contribute to the same repair/protection mechanism against NDEA-induced DNA damage but that the two mutants’ sensitivities are caused by totally unrelated metabolic deficiencies. We would thus expect, given a conjunction of both NDEA sensitivity-conferring mutant alleles in one haploid strain, an additive sensitivity to NDEA in the double mutant. By constructing haploid pso2pso7 double mutants and testing their NDEA-sensitivity we could clearly show that the two mutant alleles yielded strains more sensitive than either parental mutant alone (Table 3), i.e., they displayed additivity of sensitivities. The absence of super-sensitivity to NDEA of the double mutant (no synergistic interaction of the two mutant alleles), shows the noncompetitivity of the two metabolic "repair and protection capacities" encoded in the two respective PSO genes (Brendel and Haynes, 1973).

The analyses of all four cross-linking treatments revealed epistatic interaction of the two mutant alleles for these mutagens. In the case of 7 mM DEO even a slight protection could be detected in the double mutant and could be repeated with this and other double mutants derived from other asci from the MG5503 diploid (data not shown). This hints at a slightly different DEO metabolism in the presence of cox11-D that perhaps would lower the number of DNA-ICL lesions produced by this mutagen, thus allowing for a better survival in the absence of ICL repair. Epistatic interaction was also found after treatment with the other three ICL- forming mutagens. Sensitivity to HN2, triaziquone and to 8-MOP + UVA was identical in snm1-D single and snm1-D cox11-D double mutants, clearly showing that the reactions of these mutagens were not affected by the quality of the COX11 allele (Table 3, last three columns).

NDEA and 8HQ, but not DEO increase oxidative DNA damage in Escherichia coli tester strain WP2-IC20

Finally, we tested the hypothesis that the biotransformation of NDEA and 8HQ produces ROS that ultimately might damage DNA in pro- and eukaryotes by exposing cells of E. coli mutant WP2-IC203, known to be a reliable indicator for oxidative stress-causing chemicals (Martinez et al., 2000), to the three mutagens used in our yeast study. E. coli WP2-IC203 has a proven detection ability for mutagens that generate ROS and cause oxidative DNA damage (Blanco et al., 1998; Ohta et al., 1998) and has been successfully used in detecting such mutagens (Martinez et al., 2000).

S9-mix activated NDEA and 8HQ, but not DEO, clearly had higher mutagenicity in IC203 than in WP2 (Figure 2), which indicates a significant contribution of ROS-induced oxidative DNA lesions in mutagenesis (Martinez et al., 2000). By comparing mutagenicity with

and without metabolic activation it is clear that all three chemicals had greater mutagenic potential after biotransformation in both strains (Figure 2). NDEA is known for its high ROS production (Ahotupa et al., 1987; Boiter et al., 1995), while the mutagenicity of biotransformed 8HQ has been shown in several studies (Nagao et al., 1977; Willems et al., 1992). We might take these and our data as an indirect proof that yeast biotransformation of NDEA and 8HQ might also lead to elevated level of nitro radical intermediates and of ROS and thus to more DNA damage. In the case of the pso mutants, especially in pso3, pso6, and pso7, predicted to be susceptible to ROS-generating treatments (Querol et al., 1994; Henriques et al., 1997), this would result in a high sensitivity phenotype as indeed was found (Table 2).

CONCLUDING REMARKS

The available information on the pso mutants suggests the following grouping of these genes: four PSO genes, PSO1, PSO2, PSO4, and PSO5 encode proteins known to be involved in DNA repair which, except for PSO5, control steps in a specific error-prone recombinational repair pathway for 8-MOP photo-induced stable and highly toxic ICL. PSO3 has not yet been molecularly characterized but may encode a repair protein specific for oxidative DNA damage (Brendel et al., 1998). Two PSO genes, PSO6 and PSO7 encode proteins not involved in DNA repair but in the biosynthesis of ergosterol and in correct assembly of the mitochondrial cytochrome c oxidase (and hence allowing oxidative phosphorylation), respectively. Althoug rather detached from each other, these two metabolic activities may, each in a different way, influence the dynamics and levels of ROS that ultimately might interact with DNA. Lack of ROS-quenching effects by low ergosterol-containing membranes might be the culprit of the NDEA-sensitivity of the pso6/erg3 mutant (Schmidt et al., 1999). If this were true, a yeast cell’s sensitivity to 8HQ and to DEO would not depend on correct ergosterol content of biomembranes, since pso6/erg3 mutant has more or less WT resistance to these chemicals (Table 2). Our new data found in a sensitivity screening against NDEA, 8HQ, and DEO do not contradict but rather support our initial grouping of the PSO genes into the above-mentioned two main categories.

In summary it can be said that the PSO genes belonging to the DNA repair group have been rather important to elucidate genotoxicity (survival, repair, mutagenesis, and recombination; Henriques et al., 1997) of photo-induced psoralen DNA damage (Bankmann and Brendel, 1989), thereby controlling events that, when not properly coordinated, might eventually lead to cell death. In higher eukaryotes non-correct DNA damage processing might also lead to carcinogenesis. However, our data also point to the importance of the second group of PSO genes related to oxidative stress responses, where altered lipid composition or drug metabolism may enhance genotoxic potential (e.g., for NDEA, and to a lesser degree 8HQ, this report) and for 4NQO (Pungartnik et al., 1999). Perhaps some of the pso mutant alleles might be useful for developing yeast tester strains for selective detection of ROS-producing agents. By eliminating proteins neutralizing or destroying ROS and by partially blocking mitochondrial activity in some DNA repair mutants, yeast tester strains with a wide sensitivity range against ROS-producing chemicals could be provided.

ACKNOWLEDGMENTS

We thank C. Ayub and H. Rolla for help with experiments and M. Niesen for technical support. Research supported by CNPq and by GENOTOX. C. Pungartnik received a fellowship rom CAPES, and M. Brendel and J.A.P. Henriques recived DAAD-CNPq travel grants.

REFERENCES

Ahotupa, M., Bussacchini-Griot, V., Bereziat, J.C., Camus, A.M. and Bartsch, H. (1987). Rapid oxidative stress induced by N-nitrosamines. Biochem. Biophys. Res. Commun. 146: 1047-1054.

Bankmann, M. and Brendel, M. (1989). Molecular dosimetry of 8-MOP+UVA induced DNA-photoadducts in Saccharomyces cerevisiae: correlation of lesion number with genotoxic potential. J. Photochem. Photobiol. B: Biol 4: 57-71.

Bartsch, H., Hietanem, E. and Malaveille, C. (1989). Carcinogenic nitrosamines: free radical aspects of their action. Free Radical Biol. Med. 7: 637-644.

Blanco, M., Urios, A. and Martinez, A. (1998). New Escherichia coli WP2 tester strains highly sensitive to reversion by oxidative mutagens. Mutat. Res. 413: 95-101.

Boiter, E., Merad-Boudia, M., Guguem-Guillouzo, C., Defer, N., Ceballos-Picot, I., Lerox, J.P. and Marsac, C. (1995). Impairment of the mitochondrial respiratory chain activity in diethylnitrosamine-induced rat hepatomas: possible involvement of oxygen free radicals. Cancer Res. 55: 3028-3035.Boveris, A. (1998). Biochemistry of free radicals: from electrons to tissues. Medicina 58: 350-356.

Brendel, M. and Haynes, R.H. (1973). Interactions among genes controlling sensitivity to radiation and alkylation in yeast. Mol. Gen. Genet. 125: 197-216.

Brendel, M. and Ruhland, A. (1984). Relationships between functionality and genetic toxicology of selected DNA damaging agents. Mutat. Res. 133: 51-85.

Brendel, M., Grey, M., Maris, A.F., Hietkamp, J., Fesus, F., Pich, C.T., Dafre, L., Schmidt, M., Eckardt-Schupp, F. and Henriques, J.A.P. (1998). Low glutathione pools in the original pso3 mutant of Saccharomyces cerevisiae are responsible for its pleiotropic sensitivity phenotype. Curr. Genet. 33: 4-9.

Cassier, C., Chanet, R., Henriques, J.A.P. and Moustacchi, E. (1980). The effect of the three PSO genes on induced mutagenesis: a novel class of mutationally defective yeast. Genetics 100: 841-857.

Grey, M., Dusterhoft, A., Henriques, J.A.P. and Brendel, M. (1996). Allelism of PSO4 and PRP19 links pre-mRNA processing with recombination and error-prone DNA repair in Saccharomyces cerevisiae. Nucleic Acids Res. 24: 4009-4014.

Henriques, J.A.P. and Moustacchi, E. (1980). Isolation and characterization of pso mutants sensitive to photoaddition of psoralen derivatives in Saccharomyces cerevisiae. Genetics 95: 273-288.

Henriques, J.A.P., Vincente, E.J., da Silva, K.V.C.L. and Schenberg, A.C.G. (1989). PSO4: a novel gene involved in error-prone repair in Saccharomyces cerevisiae. Mutat. Res. 218: 111-124.

Henriques, J.A.P., Brozmanova, J. and Brendel, M. (1997). Role of PSO genes in the repair of photoinduced interstrand cross-links and photooxydative damage in the DNA of the yeast Saccharomyces cerevisiae. J. Photochem. Photobiol. B: Biol. 39: 185-196.

Hollstein, M., Talcott, R. and Wei, E. (1978). Quinoline: Conversion to a mutagen by human and rodent liver. J. Natl. Cancer Inst. 60: 405-410.

Kappus, H. and Sies, H. (1981). Toxic drug-effects associated with oxygen metabolism: redox cycling and lipid peroxidation. Experientia 37: 1233-1241.

Martinez, A., Urios, A. and Blanco, M. (2000). Mutagenicity of 80 chemicals in Escherichia coli tester strains IC203, deficient in OxyR, and its oxyR(+) parent WP2 uvrA/pKM101: detection of 31 oxidative mutagens. Mutat. Res. 467: 41-53.

Meniel, V., Magaña-Schwencke, N. and Averbeck, D. (1995). Preferential repair in yeast after induction of interstrand cross-links by 8-methoxypsoralen plus UVA. Mutat. Res. 329: 121-130.

Nagao, M., Yahagi, T., Seino, Y., Sugimura, T. and Ito, N. (1977). Mutagenicities of quinoline and its derivatives. Mutat. Res. 42: 335-342.

Ohta, T., Watanabe-Akanuma, M., Tokishita, S., Shiga, Y. and Yamagata, H. (1998). Development of new tester strains derived from E. coli WP2uvrA for the determination of mutational specificity. Mutat. Res. 413: 219-225.

Paesi-Toresan, S.O., Pich, C.T., Grey, M., Keszenman, D., Brendel, M. and Henriques, J.A.P. (1995). Gene PSO5 of Saccharomyces cerevisiae, involved in repair of oxidative damage, is allelic to RAD16. Curr. Genet. 27: 493-495.

Picada, J.N., Khromov-Borisov, N.N. and Henriques, J.A.P. (1999). Deletogenic activity of 1,2:7,8-diepoxyoctane in the Salmonella typhimurium tester strain TA102. Mutat. Res. 437: 165-173.

Pungartnik, C., Brendel, M. and Henriques, J.A.P. (1999). Mutant allele pso7-1, that sensitizes Saccharomyces cerevisiae to photoactivated psoralen, is allelic with COX11, encoding a protein indispensable for a functional cytochrome c oxidase. Curr. Genet. 36: 124-129.

Querol, C.B., Paesi-Toresan, S.O., Meira, L.B., Brendel, M. and Henriques, J.A.P. (1994). Isolation and characterization of three mutants with increased sensitivity to photoactivated 3-carbethoxypsoralen in Saccharomyces cerevisiae. Curr. Genet. 25: 407-411.

Reed, S.M., You, Z. and Friedberg, E.C. (1998). The yeast RAD7 and RAD16 genes are required for postincision events during nucleotide excision repair. J. Biol. Chem. 273: 29481-29488.

Ruhland, A., Haase, E., Siede, W. and Brendel, M. (1981a). Isolation of yeast mutants sensitive to the bifunctional alkylating agent nitrogen mustard. Mol. Gen. Genet. 181: 346-351.

Ruhland, A., Kircher, M., Wilborn, F. and Brendel, M. (1981b). A yeast mutant specifically sensitive to bifunctional alkylation. Mutat. Res. 91: 457-462.

Schmidt, C.L., Grey, M., Schmidt, M., Brendel, M. and Henriques, J.A.P. (1999). Allelism of Saccharomyces cerevisiae genes PSO6, involved in survival after 3-CPs+UVA induced damage, and ERG3, encoding the enzyme sterol C-5 desaturase. Yeast 14: 1503-1510.

Tada, M., Takahashi, K., Kawazoe, Y. and Ilto, N. (1980). Binding of quinoline to nucleic acid in a subcellular microsomal system. Chem. Biol. Interact. 29: 257-266.

Verhage, R., Zeeman, A.M., de Groot, N., Gleig, F., Bang, D.D., van de Putte, P. and Brouwer, J. (1994). The RAD7 and RAD16 genes, which are essential for pyrimidine dimer removal from the silent mating type loci, are also required for repair of the nontranscribed strand of an active gene in Saccharomyces cerevisiae. Mol. Cell. Biol. 14: 6135-6142.

Vock, E.H., Lutz, W.K., Ilinskaya, O. and Vamvakas, S. (1999). Discrimination between genotoxicity and cytotoxicity for the induction of DNA double-strand breaks in cells treated with aldehydes and diepoxides. Mutat. Res. 441: 85-93.

Wehner, E., Rao, E. and Brendel, M. (1993). Molecular structure and genetic regulation of SFA, a gene responsible for resistance to formaldehyde in Saccharomyces cerevisiae, and characterization of its protein product. Mol. Gen. Genet. 237: 351-358.

Willems, M.I., Dubois, G., Boyd, D.R., Davies, R.J.H., Hamilton, L., McCullough, J.J. and van Bladeren, P.J. (1992). Comparison of the mutagenicity of quinoline and all monohydroxyquinolines with a series of arene oxide, trans-dihydrodiol, diol epoxide, N-oxide and arene hydrate derivatives of quinoline in the Ames/Salmonella microsome test. Mutat. Res. 278: 227-236.

Wolter, R., Siede, W. and Brendel, M. (1996). Regulation of SNM1, an inducible Saccharomyces cerevisiae gene required for repair of DNA cross-links. Mol. Gen. Genet. 250: 162-168.

Yunes, M.J., Charnecki, S.E., Marden, J.J. and Millard, J.T. (1996). 1,2,5,6-diepoxyhexane and 1,2,7,8-diepoxyoctane cross-link duplex DNA at 5’-GNC sequences. Chem. Res. Toxicol. 9: 994-1000.

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