Cloning of the oxidative stress-responsive genes in Caenorhabditis elegans

oxi-1 is required for chemotaxis to odorants sensed by AWA but not AWC neurons

This study examines the role of the oxi-1 UBE3B gene in chemotaxis of C. elegans to volatile odorants. Compared to wild type worms, oxi-1 mutants showed no difference in chemotaxis to the AWC-specific odorant, isoamyl alcohol but a significant decrease in chemotaxis compared to odr-7 mutants. Both oxi-1 and odr-7 mutants exhibited significant decreases in chemotaxis to AWA-specific odorants, pyrazine and diacetyl. For thiazole, which is sensed by both AWA and AWC neurons, only odr-7 mutants showed significantly decreased chemotaxis. These data demonstrate oxi-1 is required for chemotaxis to AWA- but not AWC-specific odorants, the mechanisms of which should be investigated.

Proton Microbeam Targeted Irradiation of the Gonad Primordium Region Induces Developmental Alterations Associated with Heat Shock Responses and Cuticle Defense in Caenorhabditis elegans

We describe a methodology to manipulate Caenorhabditis elegans (C. elegans) and irradiate the stem progenitor gonad region using three MeV protons at a specific developmental stage (L1). The consequences of the targeted irradiation were first investigated by considering the organogenesis of the vulva and gonad, two well-defined and characterized developmental systems in C. elegans. In addition, we adapted high-throughput analysis protocols, using cell-sorting assays (COPAS) and whole transcriptome analysis, to the limited number of worms (>300) imposed by the selective irradiation approach. Here, the presented status report validated protocols to (i) deliver a controlled dose in specific regions of the worms; (ii) immobilize synchronized worm populations (>300); (iii) specifically target dedicated cells; (iv) study the radiation-induced developmental alterations and gene induction involved in cellular stress (heat shock protein) and cuticle injury responses that were found.

Real-Time PCR Analysis of Metabolism-Related Genes in a Long-Lived Model of C. elegans

In the nematode Caenorhabditis elegans, the mammalian tumor suppressor p53 ortholog CEP-1 (C. elegans p53-like protein) is associated not only with the stress response, germline apoptosis, and meiotic chromosome segregation but also with longevity through the modification of energy metabolism during aging. The mitochondrial respiration-related gene sco-1 in C. elegans is orthologous to the human SCO1 gene and a target of p53/CEP-1. Using quantitative real-time polymerase chain reaction (PCR) analysis, we recently found that the expression levels of sco-1 gene were increased in wild-type C. elegans in an aging-related manner and decreased in long-lived cep-1 mutants. Here, we describe the relative quantitative strategy using a commercial real-time PCR system to detect more accurately differences in the levels of expressed genes between long-lived and wild-type C. elegans strains. To estimate the expression levels of target genes compared with wild-type using relative quantification, we used the expression levels of an endogenous control gene, such as a housekeeping gene. In addition, it is critical to normalize differences in the expression levels of the common housekeeping gene among the strains analyzed for an accurate comparison of the quantitative expression levels of target genes.

In frame exon skipping in UBE3B is associated with developmental disorders and increased mortality in cattle

Background

Inherited developmental diseases can cause severe animal welfare and economic problems in dairy cattle. The use of a small number of bulls for artificial insemination (AI) carries a risk that recessive defects rapidly enrich in the population. In recent years, an increasing number of Finnish Ayrshire calves have been identified with signs of ptosis, intellectual disability, retarded growth and mortality, which constitute an inherited disorder classified as PIRM syndrome.

Results

We established a cohort of nine PIRM-affected calves and 38 unaffected half-siblings and performed a genome-wide association study (GWAS) to map the disease to a 700-kb region on bovine chromosome 17 (p = 1.55 × 10^-9). Whole genome re-sequencing of an unaffected carrier, its affected progeny and 43 other unaffected animals from another breed identified a G > A substitution mutation at the last nucleotide of exon 23 in the ubiquitin protein ligase E3B encoding gene (UBE3B). UBE3B transcript analysis revealed in-frame exon skipping in the affected animals resulting in an altered protein lacking 40 amino acids, of which 20 are located in the conserved HECT-domain, the catalytic site of the UBE3B protein. Mutation screening in 129 Ayrshire AI bulls currently used in Finland indicated a high carrier frequency (17.1%). We also found that PIRM syndrome might be connected to the recently identified AH1 haplotype, which has a frequency of 26.1% in the United States Ayrshire population.

Conclusion

We describe PIRM syndrome in cattle, which is associated with the mutated UBE3B gene. The bovine phenotype resembles human Kaufman oculocerebrofacial syndrome, which is also caused by mutations in UBE3B. PIRM syndrome might be connected with the recently identified AH1 haplotype, which is associated with reduced fertility in the US Ayrshire population. This study enables the development of a genetic test to efficiently reduce the high frequency of mutant UBE3B in Ayrshires, significantly improving animal health and reducing economic loss.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-890) contains supplementary material, which is available to authorized users.

Intracellular localization and induction of a dynamic RNA-editing event of macro-algal V-ATPase subunit A (VHA-A) in response to copper

A V-ATPase subunit A protein (VHA-A) transcript together with a variant (C793 to U), which introduces a stop codon truncating the subunit immediately downstream of its ATP binding site, was identified within a Fucus vesiculosus cDNA from a heavy metal contaminated site. This is intriguing because the VHA-A subunit is the crucial catalytic subunit responsible for the hydrolysis of ATP that drives ion transport underlying heavy metal detoxification pathways. We employed a chemiluminescent hybridization protection assay to quantify the proportion of both variants directly from mRNA while performing quantification of total transcript using Q-PCR. Polyclonal antisera raised against recombinant VHA-A facilitated simultaneous detection of parent and truncated VHA-A and revealed its cellular and subcellular localization. By exploiting laboratory exposures and samples from an environmental copper gradient, we showed that total VHA-A transcript and protein, together with levels of the truncated variant, were induced by copper. The absence of a genomic sequence representing the truncated variant suggests a RNA editing event causing the production of the truncated VHA-A. Based on these observations, we propose RNA editing as a novel molecular process underpinning VHA trafficking and intracellular sequestration of heavy metals under stress.

Impacts of chronic low-level nicotine exposure on Caenorhabditis elegans reproduction: identification of novel gene targets

Effects and mechanisms of chronic exposure to low levels of nicotine is an area fundamentally important however less investigated. We employed the model organism Caenorhabditis elegans to investigate potential impacts of chronic (24h) and low nicotine exposure (6.17-194.5 μM) on stimulus-response, reproduction, and gene expressions. Nicotine significantly affects the organism's response to touch stimulus (p=0.031), which follows a dose-dependent pattern. Chronic nicotine exposure promotes early egg-laying events and slightly increased egg productions during the first 72 h of adulthood. The expressions of 10 (egl-10, egl-44, hlh-14, ric-3, unc-103, unc-50, unc-68, sod-1, oxi-1, and old-1) out of 18 selected genes were affected significantly. Other tested genes were cat-4, egl-19, egl-47, egl-5, lin-39, unc-43, pink-1, and age-1. Changes in gene expression were more evident at low dosages than at relatively high levels. Genes implicated in reproduction, cholinergic signaling, and stress response were regulated by nicotine, suggesting widespread physiological impacts of nicotine.

Deficiency for the ubiquitin ligase UBE3B in a blepharophimosis-ptosis-intellectual-disability syndrome

Ubiquitination plays a crucial role in neurodevelopment as exemplified by Angelman syndrome, which is caused by genetic alterations of the ubiquitin ligase-encoding UBE3A gene. Although the function of UBE3A has been widely studied, little is known about its paralog UBE3B. By using exome and capillary sequencing, we here identify biallelic UBE3B mutations in four patients from three unrelated families presenting an autosomal-recessive blepharophimosis-ptosis-intellectual-disability syndrome characterized by developmental delay, growth retardation with a small head circumference, facial dysmorphisms, and low cholesterol levels. UBE3B encodes an uncharacterized E3 ubiquitin ligase. The identified UBE3B variants include one frameshift and two splice-site mutations as well as a missense substitution affecting the highly conserved HECT domain. Disruption of mouse Ube3b leads to reduced viability and recapitulates key aspects of the human disorder, such as reduced weight and brain size and a downregulation of cholesterol synthesis. We establish that the probable Caenorhabditis elegans ortholog of UBE3B, oxi-1, functions in the ubiquitin/proteasome system in vivo and is especially required under oxidative stress conditions. Our data reveal the pleiotropic effects of UBE3B deficiency and reinforce the physiological importance of ubiquitination in neuronal development and function in mammals.

Chemical dispersant potentiates crude oil impacts on growth, reproduction, and gene expression in Caenorhabditis elegans

The economic, environmental, and human health impacts of the deepwater horizon (DWH) oil spill have been of significant concern in the general public and among scientists. This study employs parallel experiments to test the effects of crude oil from the DWH oil well, chemical dispersant Corexit 9500A, and dispersant-oil mixture on growth and reproduction in the model organism Caenorhabditis elegans. Both the crude oil and the dispersant significantly inhibited the reproduction of C. elegans. Dose-dependent inhibitions of hatched larvae production were observed in worms exposed to both crude oil and dispersant. Importantly, the chemical dispersant Corexit 9500A potentiated crude oil effects; dispersant-oil mixture induced more significant effects than oil or dispersant-alone exposures. While oil-alone exposure and dispersant-alone exposure have none to moderate inhibitory effects on hatched larvae production, respectively, the mixture of dispersant and oil induced much more significant inhibition of offspring production. The production of hatched larvae was almost completely inhibited by several high concentrations of the dispersant-oil mixture. This suggests a sensitive bioassay for future investigation of oil/dispersant impacts on organisms. We also investigated the effects of crude oil/dispersant exposure at the molecular level by measuring the expressions of 31 functional genes. Results showed that the dispersant and the dispersant-oil mixture induced aberrant expressions of 12 protein-coding genes (cat-4, trxr-2, sdhb-1, lev-8, lin-39, unc-115, prdx-3, sod-1, acr-16, ric-3, unc-68, and acr-8). These 12 genes are associated with a variety of biological processes, including egg-laying, oxidative stress, muscle contraction, and neurological functions. In summary, the toxicity potentiating effect of chemical dispersant must be taken into consideration in future crude oil cleanup applications.

ROS in aging Caenorhabditis elegans: damage or signaling?

Many insights into the mechanisms and signaling pathways underlying aging have resulted from research on the nematode Caenorhabditis elegans. In this paper, we discuss the recent findings that emerged using this model organism concerning the role of reactive oxygen species (ROS) in the aging process. The accrual of oxidative stress and damage has been the predominant mechanistic explanation for the process of aging for many years, but reviewing the recent studies in C. elegans calls this theory into question. Thus, it becomes more and more evident that ROS are not merely toxic byproducts of the oxidative metabolism. Rather it seems more likely that tightly controlled concentrations of ROS and fluctuations in redox potential are important mediators of signaling processes. We therefore discuss some theories that explain how redox signaling may be involved in aging and provide some examples of ROS functions and signaling in C. elegans metabolism. To understand the role of ROS and the redox status in physiology, stress response, development, and aging, there is a rising need for accurate and reversible in vivo detection. Therefore, we comment on some methods of ROS and redox detection with emphasis on the implementation of genetically encoded biosensors in C. elegans.

Interactions of bacterial proteins with host eukaryotic ubiquitin pathways

Ubiquitination is a post-translational modification in which one or more 76 amino acid polypeptide ubiquitin molecules are covalently linked to the lysine residues of target proteins. Ubiquitination is the main pathway for protein degradation that governs a variety of eukaryotic cellular processes, including the cell-cycle, vesicle trafficking, antigen presentation, and signal transduction. Not surprisingly, aberrations in the system have been implicated in the pathogenesis of many diseases including inflammatory and neurodegenerative disorders. Recent studies have revealed that viruses and bacterial pathogens exploit the host ubiquitination pathways to gain entry and to aid their survival/replication inside host cells. This review will summarize recent developments in understanding the biochemical and structural mechanisms utilized by bacterial pathogens to interact with the host ubiquitination pathways.

Reactive Oxygen Species and Aging in Caenorhabditis elegans: Causal or Casual Relationship?

The free radical theory of aging proposes a causal relationship between reactive oxygen species (ROS) and aging. While it is clear that oxidative damage increases with age, its role in the aging process is uncertain. Testing the free radical theory of aging requires experimentally manipulating ROS production or detoxification and examining the resulting effects on lifespan. In this review, we examine the relationship between ROS and aging in the genetic model organism Caenorhabditis elegans, summarizing experiments using long-lived mutants, mutants with altered mitochondrial function, mutants with decreased antioxidant defenses, worms treated with antioxidant compounds, and worms exposed to different environmental conditions. While there is frequently a negative correlation between oxidative damage and lifespan, there are many examples in which they are uncoupled. Neither is resistance to oxidative stress sufficient for a long life nor are all long-lived mutants more resistant to oxidative stress. Similarly, sensitivity to oxidative stress does not necessarily shorten lifespan and is in fact compatible with long life. Overall, the data in C. elegans indicate that oxidative damage can be dissociated from aging in experimental situations.

SOD-1 deletions in Caenorhabditis elegans alter the localization of intracellular reactive oxygen species and show molecular compensation

Superoxide dismutase (SOD) is an enzyme that catalytically removes the superoxide radical (*O2-) and protects organisms from oxidative damage during normal aging. We demonstrate that not only the cytosolic *O2- level but also the mitochondrial *O2- level increases in the deletion mutants of sod-1 gene encoding Cu/Zn SOD in Caenorhabditis elegans (C. elegans). Interestingly, this suggests that the activity of SOD-1, which so far has been thought to act mainly in cytoplasm, helps to control the detoxification of *O2- also in the mitochondria. We also found functional compensation by other SODs, especially the sod-5 gene, which was induced several fold in the mutants. Therefore, the possibility exists that the compensative expression of sod-5 gene in the sod-1 deficit is associated with the insulin/insulin-like growth factor-1 (Ins/IGF-1) signaling pathway, which regulates longevity and stress resistance of C. elegans because the sod-5 gene may be a target of the pathway.

Prolonged manganese exposure induces severe deficits in lifespan, development and reproduction possibly by altering oxidative stress response in Caenorhabditis elegans

We examined the possible multiple defects induced by acute and prolonged exposure to high levels of manganese (Mn) solution by monitoring the endpoints of lifespan, development, reproduction, and stress response. Our data suggest that acute exposure (6 h) to Mn did not cause severe defects of life span, development, and reproduction, similarly, no significant defect could be found in animals exposed to a low concentration of Mn (2.5 micromol/L) for 48 h. In contrast, prolonged exposure (48 h) to high Mn concentrations (75 and 200 micromol/L) resulted in significant defects of life span, development, and reproduction, as well as the increase of the percentage of population with hsp-16.2::gfp expression indicating the obvious induction of stress responses in exposed animals. Moreover, prolonged exposure (48 h) to high concentrations (75 and 200 micromol/L) of Mn decreased the expression levels of antioxidant genes of sod-1, sod-2, sod-3, and sod-4 compared to control. Therefore, prolonged exposure to high concentrations of Mn will induce the severe defects of life span, development, and reproduction in nematodes possibly by affecting the stress response and expression of antioxidant genes in Caenorhabditis elegans.

Hyperoxia exposure induced hormesis decreases mitochondrial superoxide radical levels via Ins/IGF-1 signaling pathway in a long-lived age-1 mutant of Caenorhabditis elegans

The hormetic effect, which extends the lifespan by various stressors, has been confirmed in Caenorhabditis elegans (C. elegans). We have previously reported that oxidative stress resistance in a long-lived mutant age-1 is associated with the hormesis. In the age-1 allele, which activates an insulin/insulin-like growth factor-1 (Ins/IGF-1) signaling pathway, the superoxide dismutase (SOD) and catalase activities increased during normal aging. We now demonstrate changes in the mitochondrial superoxide radical (*O(2)(-)) levels of the hormetic conditioned age-related strains. The *O(2)(-) levels in age-1 strain significantly decreased after intermittent hyperoxia exposure. On the other hand, this phenomenon was not observed in a daf-16 null mutant. This hormesis-dependent reduction of the *O(2)(-) levels was observed even if the mitochondrial Mn-SOD was experimentally reduced. Therefore, it is indicated that the hormesis is mediated by events that suppress the mitochondrial *O(2)(-) production. Moreover, some SOD gene expressions in the hormetic conditioned age-1 mutant were induced over steady state mRNA levels. These data suggest that oxidative stress-inducible hormesis is associated with a reduction of the mitochondrial *O(2)(-) production by activation of the antioxidant system via the Ins/IGF-1 signaling pathway.

The inflammation‐associatedSalmonellaSopA is a HECT‐like E3 ubiquitin ligase

Salmonella translocate a group of type III effectors into the host cells to induce entry, promote survival and cause intestinal inflammation. Although the biochemical and cellular mechanisms of how bacterial effectors function inside host cells remain largely unknown, studies have indicated that a likely strategy is to exploit host cellular pathways through functional mimicry. We report here that SopA, a Salmonella type III effector, mimics the mammalian HECT E3 ubiquitin ligase. SopA preferentially uses the host UbcH5a, UbcH5c and UbcH7 as E2s, which are involved in inflammation. Both the wild-type SopA and the mutant SopAC753S were expressed and translocated at similar levels during the infection of HeLa cells. A Salmonella strain expressing a catalytically incompetent SopAC753S mutant had reduced Salmonella-induced polymorphonuclear leukocytes transepithelial migration. We speculate that SopA ubiquitinate bacterial/host proteins involved in Salmonella-induced intestinal inflammation.

Complex II inactivation is lethal in the nematode Caenorhabditis elegans

RNA-mediated interference (RNAi) was employed to systematically inactivate the four subunits of complex II in the mitochondrial electron transport chain. Embryonic lethality was the predominant result of inactivating three subunits (ceSDHB, ceSDHC, and ceSDHD) when using the soaking method to inactivate RNA. The feeding method was employed to deliver dsRNA from the fourth subunit (ceSDHA) to wild-type, mev-1 (mutated in ceSDHC of complex II), and gas-1 animals (mutated in a complex I gene). Survival was reduced only in the mev-1 genetic background, and in an oxygen-dependent fashion. Collectively, these data provide further evidence that compromised complex II integrity can result in sensitivity to oxidative stress.

Human targets of Pseudomonas aeruginosa pyocyanin

Pseudomonas aeruginosa produces copious amounts of the redoxactive tricyclic compound pyocyanin that kills competing microbes and mammalian cells, especially during cystic fibrosis lung infection. Cross-phylum susceptibility to pyocyanin suggests the existence of evolutionarily conserved physiological targets. We screened a Saccharomyces cerevisiae deletion library to identify presumptive pyocyanin targets with the expectation that similar targets would be conserved in humans. Fifty S. cerevisiae targets were provisionally identified, of which 60% have orthologous human counterparts. These targets encompassed major cellular pathways involved in the cell cycle, electron transport and respiration, epidermal cell growth, protein sorting, vesicle transport, and the vacuolar ATPase. Using cultured human lung epithelial cells, we showed that pyocyanin-mediated reactive oxygen intermediates inactivate human vacuolar ATPase, supporting the validity of the yeast screen. We discuss how the inactivation of V-ATPase may negatively impact the lung function of cystic fibrosis patients.

Characterization of the human UBE3B gene: structure, expression, evolution, and alternative splicing

E3 ubiquitin ligases target proteins for degradation by adding ubiquitin residues. We characterized full-length cDNAs for human and mouse UBE3B, a novel HECT-domain E3 ligase, and analyzed the structure of human UBE3B on chromosome 12q24.1. Alternative splicing of exon 20 of UBE3B generated two major transcripts. The 5.7-kb mRNA lacked exon 20 and encoded a full-length protein ligase, variant 1 (UBE3B_v1). A second transcript contained a 97-bp insertion encoded by exon 20 that introduced an in-frame stop codon. The predicted protein (UBE3B_v2) would lack the HECT domain and would be nonfunctional, since the HECT domain constitutes the active site for ubiquitin transfer. No alternative splicing was observed in this region of mouse UBE3B. Elimination of the HECT domain by alternative splicing has not been reported in any genes encoding HECT domain ligases and may represent a novel mechanism in regulating intracellular levels of functional HECT-domain ligases.

Tissue-specific expression, heat inducibility, and biological roles of two hsp16 genes in Caenorhabditis elegans

In this report we have examined two new heat shock protein (HSP16) proteins in the nematode Caenorhabditis elegans encoded by the open reading frames F08H9.3 and F08H9.4. The F08H9.3 and F08H9.4 genes are oriented in the same direction next to each other on the chromosome, not sharing any promoter region, unlike other hsp16 genes that share common promoters in pairs. The F08H9.3 and F08H9.4 proteins were expressed in a tissue-specific manner, unlike the other four HSP16 proteins. F08H9.3 was expressed in the pharynx, and F08H9.4 in the excretory canal and a few neuronal cells. While F08H9.3 was weakly induced by heat shock only in the same tissue as under the normal condition, F08H9.4 was newly induced in the intestine. RNA interference experiments showed that these two proteins are required for survival under the heat shock condition.

Adaptive responses to oxidative damage in three mutants of Caenorhabditis elegans (age-1, mev-1 and daf-16) that affect life span

Oxidative damage shortens the life span of the nematode Caenorhabditis elegans (C. elegans), even in an age-1 mutant that is characterized by a long life and oxygen resistance. We found that daily short-term exposure (3 h) to hyperoxia further extended the life span of age-1, a phenomenon known as an adaptive response. age-1 also showed resistance to paraquat and heat. Acute hyperoxic treatment did not extend the life spans of wild type, daf-16 or mev-1. daf-16 mutant had a slightly shorter life span compared to wild type and was sensitive to heat and paraquat. The daf-16 phenotype resembles that of mev-1 showing a short life and oxygen sensitivity. We measured mRNA levels of superoxide dismutase genes (sod-1 through 4), catalase genes (clt-1 and ctl-2), known to encode anti-oxidant enzymes, and found they were elevated in age-1 young adults. On the other hand, in daf-16 and mev-1, the expression of sod-1, sod-2 and sod-3 genes was lower rather than in wild type. Conversely, ctl-1 and ctl-2 genes expression was significantly elevated in daf-16 and mev-1. This suggests that DAF-16, a forkhead/winged-helix transcription factor, whose expression is suppressed by AGE-1, phosphoinositide 3-kinase (PI3-kinase), regulates anti-oxidant genes as well as energy metabolism under atmospheric conditions. However, the level of gene expression of SOD and catalase was not elevated by short-term exposure to 90% oxygen in wild type, mev-1, daf-16 and even age-1. This suggests that SOD and catalase do not play a role in the adaptive response against oxidative stress under hyperoxia, at least under these experimental conditions.

Characterization of spontaneous mutation in the delta soxR and SoxS overproducing strains of Escherichia coli

To examine the role of the soxRS regulon in mutagenesis, we characterized the spontaneous mutations occurring in the endogenous tonB gene in the delta soxR strain and the SoxS overproducing strain of Escherichia coli. Neither the delta soxR strain nor the SoxS overproducing strain led to an enhancement or diminishment of the spontaneous mutation frequency. By DNA sequencing, we determined 50 spontaneous mutants from the delta soxR strains, and found that 36% were both base substitutions and IS insertions, 14% frameshifts and 10% deletions. Among the base substitutions, G:C-->T:A transversions and G:C-->A:T transitions predominated, followed by A:T-->T:A transversions. We determined 54 spontaneous mutants from the SoxS overproducing strains, and found that 37% were IS insertions, 31% base substitutions, 17% frameshifts, 9% deletions and 6% duplications. Among the base substitutions, G:C-->T:A transversions dominated, followed by A:T-->T:A transversions and G:C-->A:T transitions. These results were similar to those from the soxRS+ strains. Thus, it is suggested that the soxRS-regulated genes do not play a significant role in the defense against spontaneous mutagenesis.

Identification of some heat-induced genes of Trichinella spiralis

Three heat-induced genes of the infective-stage larvae of Trichinella spiralis were successfully identified by the suppression subtractive hybridization (SSH) technique. As indicated by reverse Northern blotting, 19 of 25 clones were scored as differentially transcribed in the heat-shocked infective-stage larvae. The sequencing data showed the presence of 12 different genes. Three were homologous to histone H3, histone H2B and translationally controlled tumour protein (TCTP). A 0.6 kb cDNA of histone H3 was generated by the RACE method and sequenced. It contained an open reading frame of 136 amino acids that demonstrated 94% identity with genes from Drosophila hydei. Semi-quantitative RT-PCR indicated that after heat-shock treatment, the expression levels of histone H3, histone H2B and TCTP increased 4.8, 27 and 5.7-fold, respectively. Northern analysis confirmed the upregulation of histone H3, histone H2B and TCTP transcripts. The upregulation of these genes during stress conditions has not been reported in parasitic organisms. The stress proteins may play an active role to sustain the parasite after exposure to hostile host factors.

Role of the Escherichia coli and human DNA glycosylases that remove 5-formyluracil from DNA in the prevention of mutations

Ionizing radiation induces a wide variety of modifications to purine and pyrimidine residues. The exocyclic methyl group of thymine does not escape oxidative damage. Any 5-hydroperoxymethyluracil produced is spontaneously decomposed to form 5-formyluracil (5-foU) and 5-hydroxymethyluracil. The yield of 5-foU by ionizing radiation is roughly the same as that of 8-oxoguanine. 5-foU is a potential mutagenic damage in vitro and in vivo. Mammalian cells have an activity that removes 5-foU from X-irradiated DNA. Furthermore, the Nth, Nei and MutM proteins of E. coli have DNA glycosylase/AP lyase activities that recognize and remove 5-foU in DNA. The mutation frequency of 5-foU-containing plasmid increases when replicated in E. coli nthneimutMalkA. Single mutations in the nth, nei or mutM gene do not affect the mutation frequency. Therefore, these gene products are likely backup enzymes used to repair 5-foU in DNA. Furthermore, the human hNTH1 enzyme, a homologue of E. coli Nth, is found to have similar DNA glycosylase activity to that of the Nth protein.

2-hydroxyadenine in DNA is a very poor substrate of the Escherichia coli MutY protein

To test the possibility that the Escherichia coli MutY or MutM protein acts as a 2-hydroxyadenine (2-OH-Ade) glycosylase, we treated double-stranded oligodeoxyribonucleotides containing 2-OH-Ade with the E. coli MutY or MutM protein in vitro. We found that a strand with 2-OH-Ade was a very poor substrate of MutY, irrespective of the base in the complementary strand. Moreover, a strand containing adenine or guanine opposite 2-OH-Ade was also rarely cleaved by MutY. The cleavage of oligonucleotides with 2-OH-Ade by MutM was not observed. These results indicate that neither MutY nor MutM plays an important role in the removal of 2-OH-Ade from DNA.

Oxidative stress pretreatment increases the X-radiation resistance of the nematode Caenorhabditis elegans

Pre-exposure of wild-type Caenorhabditis elegans to oxygen conferred a protective effect against the lethality imposed by subsequent X-irradiation. In contrast, two mutants (rad-1 and rad-2) that are UV and ionizing radiation hypersensitive but not oxygen sensitive, did not exhibit this adaptive response. To explore the molecular basis of protection, the expression of several key genes was examined using Northern blot analyses to measure mRNA levels. In the wild-type, expression of the heat shock protein genes, hsp16-1 and hsp16-48, increased dramatically after incubation under high oxygen. Expression of two superoxide dismutase genes (sod-1 and sod-3) was relatively unaffected. Unlike the wild-type, the basal levels of these four genes were significantly lower in the rad-1 and rad-2 mutants under atmospheric conditions. These genes were partially induced in response to oxidative stress. These data suggest that at least a portion of the hypersensitive phenotype of rad-1 and rad-2 may be attributed to inappropriate gene expression.