Polypyrrole-based nanomaterials: A novel strategy for reducing toxic chemicals and others related to environmental sustainability applications

Aqueous contaminants such as pharmaceuticals, dyes, personal care products, etc., are the common water contaminants that show adverse health effects. Photocatalysis is one of the well-known techniques to treat these water contaminants. Currently, most inorganic photocatalysts show a poor balance between adsorption and photocatalytic activity. In addition, heavy metal pollution and low biosafety are significant concerns in photocatalysis. Thus, environmentally friendly photocatalysts are required to avoid the secondary pollution caused by some inorganic semiconductor-photocatalysts. Organic polymer-based photocatalysts are low-cost, stable, non-toxic, and can utilize visible and NIR light for photocatalysis. In this review, we have discussed polypyrrole as a photocatalyst. Polypyrrole is a conducting organic polymer photocatalyst that is highly stable with high charge mobility and strong binding sites for photocatalytic reactions. Besides these advantages, polypyrrole has limitations, such as high charge recombination due to a small bandgap and poor dispersity. So we have explored the modifications to polypyrrole photocatalysts, such as doping and heterojunctions. Further, we have explained the applications of polypyrrole in photocatalysis as an adsorbent, sensitizer, degradation of pollutants, and energy production. Finally, the future aspects of polypyrrole photocatalysis are also explored to improve the path of future research.

Advanced electro-Fenton degradation of a mixture of pharmaceutical and steel industrial wastewater by pallet-activated-carbon using three-dimensional electrode reactor

In the present work, a three-dimensional electrode reactor (3Der) using pallet activated carbon (PAC), as particle electrodes, was investigated to degrade non-biodegradable organic pollutants in pharmaceutical wastewater and steel industry wastewater. The effect of operating parameters, such as pH, electrode distance, O₂ flow rate, and current density was investigated. The TOC removal efficiency in 3Der was achieved at the highest mineralization yield of 94.1% after 180 min electrolysis, which was 10-19% higher than the two-dimensional electrode reactor (2Der). The higher performance of the 3Der can be attributed to the indirect and direct oxidation mechanisms. The impact of supporting electrolytes was decreased in order as chloride > nitrate > sulfate. The morphology of sludge and the presence of Fe(OH)₃ after Fenton-oxidation were investigated. 3Der system improved biodegradability of pharmaceutical wastewater after electro-Fenton treatment at a PW/SIW ratio of 3:1 (BOD₅/COD = 0.6). Hence, the mechanism of 3Der/PAC, as particle electrodes was also proposed. 3Der with PAC particle electrodes using steel industry wastewater as a catalyst is an exciting technique for remediation of organic contaminated pharmaceutical wastewater.

The practicality and prospects for disinfection control by photocatalysis during and post-pandemic: A critical review

The prevalence of global health implications from the COVID-19 pandemic necessitates the innovation and large-scale application of disinfection technologies for contaminated surfaces, air, and wastewater as the significant transmission media of disease. To date, primarily recommended disinfection practices are energy exhausting, chemical driven, and cause severe impact on the environment. The research on advanced oxidation processes has been recognized as promising strategies for disinfection purposes. In particular, semiconductor-based photocatalysis is an effective renewable solar-driven technology that relies on the reactive oxidative species, mainly hydroxyl (•OH) and superoxide (•O₂^-) radicals, for rupturing the capsid shell of the virus and loss of pathogenicity. However, the limited understanding of critical aspects such as viral photo-inactivation mechanism, rapid virus mutagenicity, and virus viability for a prolonged time restricts the large-scale application of photocatalytic disinfection technology. In this work, fundamentals of photocatalysis disinfection phenomena are addressed with a reviewed remark on the reported literature of semiconductor photocatalysts efficacies against SARS-CoV-2. Furthermore, to validate the photocatalysis process on an industrial scale, we provide updated data on available commercial modalities for an effective virus photo-inactivation process. An elaborative discussion on the long-term challenges and sustainable solutions is suggested to fill in the existing knowledge gaps. We anticipate this review will ignite interest among researchers to pave the way to the photocatalysis process for disinfecting virus-contaminated environments and surfaces for current and future pandemics.

Modified compact fluorescent lamps improve light-induced off-season floral stimulation in dragon fruit farming

Efficient light-induced floral stimulation plays a key role in energy conservation and maintaining stable productivity during off-season periods of dragon fruit plants. In this study, we first reported on results of a survey on dragon fruit farmers regarding use of lamps in performing artificially induced flowering process in Vietnam. It was found that the use of incandescent lamp was prevalent in dragon fruit cultivation practices, resulting in heavy electricity consumption, and that low-power compact fluorescent light (CFL) bulbs were not extensively utilized, possibly due to low floral induction performance of domestic CFL bulbs. Arguing that emission spectra of currently used lamps were not consistent with adsorption spectra of phytochromes, whose transformation is responsible for flowering process of dragon fruit, we then proposed three improved CFL lamps (power capacity of 20 W) having emission spectra focused on red and far-red regions. New lamp prototypes were tested in 7 field experiments in three different provinces in Vietnam. One improved CFL bulb (treatment 2) performed relatively well in comparison with the incandescent control lamp (60 W) in six out of seven experiments with regard to some growth indicators (e.g., number of floral stems, number of bubs, number of fruits per plant) and fruit yield. Recent success on commercialization of the improved CFL lamp demonstrates the potential of CFL lamps in floral stimulating irradiation of other crops and plants and in alleviating electricity burden in dragon fruit growing areas.

Effects of microwave blanching conditions on the quality of green asparagus (Asparagus officinalis L.) butt segment

Blanching is a pretreatment method that is often applied in fruit and vegetable processing to inhibit enzyme activity and reduce loss of food quality. It was recently discovered that well-controlled microwave volumetric heating could improve the blanching efficiency and retain nutritional and sensorial values of product. This study was conducted to investigate effects of microwave blanching conditions on the quality of green asparagus (Asparagus officinalis L.) butt segments, a rich source of fiber and antioxidants but are often discarded during processing. The experiments were designed by one-factor-at-a-time method with two varying factors including blanching time (2, 4, 6, and 8 min) and microwave power output (150, 300, 450, and 600 W). Quality of product was evaluated by sensory, retention of phenolics, and free-radical scavenging activity retention. The results showed that longer blanching time or higher microwave power was associated with reduced quality of green asparagus butt segment. Besides, the appropriate parameters for microwave blanching of the green asparagus butt segment was found at 300 W for 4 min.

Functional Magnetic Core-Shell System-Based Iron Oxide Nanoparticle Coated with Biocompatible Copolymer for Anticancer Drug Delivery

Polymer coating has drawn increasing attention as a leading strategy to overcome the drawbacks of superparamagnetic iron oxide nanoparticles (SPIONs) in targeted delivery of anticancer drugs. In this study, SPIONs were modified with heparin-Poloxamer (HP) shell to form a SPION@HP core-shell system for anticancer drug delivery. The obtained formulation was characterized by techniques including transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), vibration sample magnetometer (VSM), proton nuclear magnetic resonance (¹H-NMR), and powder X-ray diffraction (XRD). Results showed the successful attachment of HP shell on the surface of SPION core and the inability to cause considerable effects to the crystal structure and unique magnetic nature of SPION. The core-shell system maintains the morphological features of SPIONs and the desired size range. Notably, Doxorubicin (DOX), an anticancer drug, was effectively entrapped into the polymeric shell of SPION@HP, showing a loading efficiency of 66.9 ± 2.7% and controlled release up to 120 h without any initial burst effect. Additionally, MTT assay revealed that DOX-loaded SPION@HP exerted great anticancer effect against HeLa cells and could be safely used. These results pave the way for the application of SPION@HP as an effective targeted delivery system for cancer treatment.

Fatty Acid, Lipid Classes and Phospholipid Molecular Species Composition of the Marine Clam Meretrix lyrata (Sowerby 1851) from Cua Lo Beach, Nghe An Province, Vietnam

This study aims to analyze compositions of fatty acids and phospholipid molecular species in the hard clams Meretrix lyrata (Sowerby, 1851) harvested from Cua Lo beach, Nghe An province, Viet Nam. Total lipid of hard clams Meretrix lyrata occupied 1.7 ± 0.2% of wet weight and contained six classes: hydrocarbon and wax (HW), triacylglycerol (TAG), free fatty acids (FFA), sterol (ST), polar lipid (PoL), and monoalkyl diacylglycerol (MADAG). Among the constituents, the proportion of PoL accounted was highest, at 45.7%. In contrast, the figures for MADAG were lowest, at 1.3%. Twenty-six fatty acids were identified with the ratios of USAFA/SAFA was 2. The percentage of n-3 PUFA (ω-3) and n-6 PUFA (ω-6) was high, occupying 38.4% of total FA. Among PUFAs, arachidonic acid (AA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3), docosapentaenoic acid (DPA, 22:5n-3), and docosahexaenoic acid (DHA, 22:6n-3) accounted for 3.8%, 7.8%, 2.2% and 12.0% of total lipid of the clam respectively. Phospholipid molecular species were identified in polar lipids of the clams consisting six types: phosphatidylethalnolamine (PE, with 28 molecular species), phosphatidylcholine (PC, with 26 molecular species), phosphatidylserine (PS, with 18 molecular species), phosphatidylinositol (PI, with 10 molecular species), phosphatidylglycerol (PG, with only one molecular species), and ceramide aminoethylphosphonate (CAEP, with 15 molecular species). This is the first time that the molecular species of sphingophospholipid were determined, in Meretrix lyrata in particular, and for clams in general. Phospholipid formula species of PE and PS were revealed to comprise two kinds: Alkenyl acyl glycerophosphoethanolamine and Alkenyl acyl glycerophosphoserine occupy 80.3% and 81.0% of total PE and PS species, respectively. In contrast, the percentage of diacyl glycero phosphatidylcholine was twice as high as that of PakCho in total PC, at 69.3, in comparison with 30.7%. In addition, phospholipid formula species of PI and PG comprised only diacyl glycoro phospholipids. PE 36:1 (p18:0/18:1), PC 38:6 (16:0/22:6), PS 38:1 (p18:0/20:1), PI 40:5 (20:1/20:4), PG 32:0 (16:0/16:0) and CAEP 34:2 (16:2/d18:0) were the major molecular species.

E2F-1 represses transcription of the human telomerase reverse transcriptase gene

The ends of human chromosomes (telomeres) lose up to 200 bp of DNA per cell division. Chromosomal shortening ultimately leads to senescence and death in normal cells. Many human carcinoma lines are immortal in vitro, suggesting that these cells have a mechanism for maintaining the ends of their chromosomes. Telomerase is a ribonucleoprotein complex that synthesizes telomeric DNA onto chromosomes using its RNA component as template. Telomerase activity is found in most tumor cells, but is absent from normal cells. Little is known about how normal human cells repress telomerase (hTERT) gene expression. Mice carrying an E2F-1 null mutation develop a variety of malignant tumors, suggesting that this transcription factor has a tumor suppressor function. To determine mechanisms by which E2F-1 suppresses tumor formation, we examined the role of this transcription factor in regulation of the hTERT promoter in human cells. We identified two putative E2F-1-binding sites proximal to the transcriptional start site of the hTERT promoter. Mutation of these sites produced dramatic increases in promoter activity. Overexpression of E2F-1 but not a mutant E2F-1 repressed hTERT promoter activity in reporter gene assays. This repression was abolished by mutation of the E2F-1-binding sites in the hTERT promoter. Human cancer cell lines stably overexpressing E2F-1 exhibited decreased hTERT mRNA expression and telomerase activity. We conclude that E2F-1 has an atypical function as a transcriptional repressor of the hTERT gene in human cells.

Rb and E2F-1 regulate telomerase activity in human cancer cells

The ends of human chromosomes (telomeres) lose up to 200 bp of DNA per cell division. Chromosomal shortening ultimately leads to senescence and death in normal cells. Many human carcinoma lines are immortal in vitro, suggesting that these cells have a mechanism for maintaining the ends of their chromosomes. Telomerase is a ribonucleoprotein complex that synthesizes telomeric DNA onto chromosomes using its RNA component as a template. Recent studies have shown that inactivation of the retinoblastoma gene product pRb and the cyclin dependent kinase inhibitor p16(INK4A) is required for telomerase activity in epithelial cells. We have demonstrated previously that restoration of functional retinoblastoma (Rb) expression is sufficient to downregulate telomerase activity in carcinoma cells. To determine mechanisms by which Rb regulates telomerase expression, we examined the effects of cyclin dependent kinase (cdk) mediated Rb inactivation and the release of E2F-1 on telomerase activity in human carcinoma cells. Overexpression of cdk2 and cdk4 but not a dominant negative cdk2 rescued Rb mediated downregulation of telomerase activity. Overexpression of the cdk regulatory subunit cyclin D1 also rescued telomerase downregulation and p16 expression alone was sufficient to ablate activity. E2F-1 overexpression was sufficient to rescue Rb mediated reduction of telomerase activity, but an E2F-1 mutant defective in DNA and Rb binding activities failed to produce this effect. Tumor tissue from E2F-1 -/- mice was negative for telomerase activity, indicating a key regulatory role for this transcription factor.

Giant cell formation in cells exposed to 740 nm and 760 nm optical traps

BACKGROUND AND OBJECTIVE

Optical trapping is becoming a useful and widespread technique for the micromanipulation of cells and organelles. Giant cell formation following optical trapping was studied to detect the potential adverse effects.

STUDY DESIGN/MATERIALS AND METHODS

The nuclei of preselected single CHO cells were exposed to 740 nm and 760 nm laser microbeam generated by a titanium-sapphire tunable laser at 88 and 176 mW and different time exposures. The irradiated single cells were recorded and observed morphologically following exposure. Giant cells were tabulated and photographed.

RESULTS

The irradiated cells either failed to divide, or they underwent nuclear proliferation to form giant cells through endoreduplication.

CONCLUSION

Giant cells were induced by both 740 nm and 760 nm. The frequency of giant cell formation was higher for the longer time exposures and at the higher power densities. The use of an optical etalon to remove intracavity mode beating and high peak powers of the titanium-sapphire laser caused a significant reduction in the formation of giant cells.

Subcellular phototoxicity of 5-aminolaevulinic acid (ALA)

BACKGROUND AND OBJECTIVE

5-aminolaevulinic acid (ALA) is a new, promising photosensitizer for PDT of cancer. Subcellular toxicity induced by ALA and light exposure in single cells was studied to elucidate the mechanism of cell damage.

STUDY DESIGN/MATERIALS AND METHODS

CPAE, PTK2, and rat neonatal myocardial cells treated with ALA were examined for localization using fluorescence microscopy and for subcellular phototoxicity using 630 nm laser microbeam irradiation of specific subcellular regions.

RESULTS

In CPAE and PTK2 cells, a large amount of fluorescence was detected in the peri-nuclear cytoplasm. In rat neonatal myocardial cells, the sensitizer selectively localized in the large mitochondria. In both cell types, there was little phototoxicity when the peripheral cytoplasmic region was exposed, as compared to considerable phototoxicity with exposure of either the perinuclear or nuclear regions.

CONCLUSION

Both the CPAE and PTK2 cells demonstrated that the nucleus followed by the perinuclear cytoplasm are the most sensitive cell areas with no sensitivity in the peripheral cytoplasm.

Intact functional domains of the retinoblastoma gene product (pRb) are required for downregulation of telomerase activity

The ends of human chromosomes (telomeres) consist of tandem repeats of the sequence TTAGGG. Telomeres lose up to 200 base pairs of DNA per cell division due to the inability of DNA polymerase to completely replicate the chromosomal ends. Chromosomal shortening ultimately leads to senescence and cell death in normal cells. However, some immortal cells do not lose telomeric sequence during DNA replication. Many human carcinoma lines are immortal in vitro, suggesting that these cells have a mechanism for maintaining the ends of their chromosomes. Telomerase is a ribonucleoprotein complex that synthesizes telomeric DNA onto chromosomes using its RNA component as a template. To elucidate potential mechanisms for telomerase regulation, we tested human squamous cell carcinoma lines (SCCs) for telomerase activity. All SCC lines expressed high levels of telomerase activity. Synchronization in specific cell cycle phases caused marked reduction in telomerase activity in G0 and S, but not in G1 or M. Reduction in telomerase activity correlated with induction of Rb protein in these phases. Overexpression of full length Rb resulted in significant downregulation of telomerase activity. However, expression of an Rb N-terminal oligomerization domain deletion construct, a C-terminal DNA binding domain deletion construct, or a pocket domain mutant failed to downregulate telomerase activity. We concluded that functionally intact Rb was required for cell cycle-dependent downregulation of telomerase activity in SCC lines.

Postanginal septicaemia with external jugular venous thrombosis: case report

Postanginal septicaemia is a syndrome of anaerobic septicaemia, septic thrombophlebitis of the internal jugular vein, and metastatic infections, that follows a localized infection in the area drained by the large cervical veins. The syndrome was well-known and often fatal in the preantibiotic era. It is now rather rare, presumably as a result of the almost routine use of prophylactic antibiotics. The symptoms are classic, and it should be suspected in any case where septicaemia and metastatic lesions are preceded by a head and neck infection. We report a case that is typical, except that branches of the external jugular vein were thrombosed. To our knowledge this has not been reported previously.

Novel germline mutations of the MEN1 gene in Japanese patients with multiple endocrine neoplasia type 1

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterized by tumors of the parathyroid glands, the pancreatic islet cells, and the anterior pituitary. Germline mutations of the MEN1 gene in three independent Japanese cases with MEN1 were analyzed. Case 1 has revealed a 2-bp (TA) insertion at nucleotide position 341 (341insTA) in exon 2, which shifts the reading frame such that the mutant protein has a completely different amino acid sequence from codon 78 to the premature stop codon at 119. In case 2, a nucleotide substitution, i.e., TAG in place of TGG, which encodes tryptophan at codon 198 was identified (nonsense mutation). These mutations were heterozygously present and have not been reported previously. Case 3 showed no mutations in the protein-coding exons and exon-intron junctions of the MEN1 gene by single-strand conformation polymorphism or direct sequencing of the polymerase chain reaction (PCR) fragments. We confirmed the finding that patients with MEN1 carry heterozygous germline mutations in the MEN1 gene, which is compatible with the idea that the MEN1 gene is a tumor suppressor gene. The reason why mutations in the coding region of the MEN1 gene could not be detected by PCR-based analysis in some of the MEN1 patients, e.g. case 3, needs to be clarified further.

Defective mismatch repair in extracts of colorectal and endometrial cancer cell lines exhibiting microsatellite instability

A replication error (RER+) phenotype, characterized by somatic instability in simple repeated sequences, is associated with several types of cancer. To determine if a defect in DNA replication fidelity or repair of replication errors might explain this instability, we compared both processes in cell-free extracts from RER+ endometrial and colorectal cancer cell lines to RER- cell lines. SV40 origin-dependent replication of a microsatellite sequence is highly accurate in cell extracts regardless of their RER phenotype. However, extracts from RER+ cell lines are defective in mismatch repair, while extracts of RER- cell lines are not. Lack of repair was observed when the signal (a nick) for strand-specific repair was either 3' or 5' to the mispair. One colorectal cancer cell line contained deletions in both alleles of the putative mismatch repair gene hMSH2, and one endometrial cancer cell line contained a 4-base pair duplication in one hMSH2 allele. No hMSH2 mutation was detected in the other allele or in the other five RER+ cell lines. Repair was readily detected when each of the defective extracts was mixed with a repair-proficient extract, demonstrating that no trans-acting inhibitor is present. Attempts to complement the repair deficiencies by mixing two different defective extracts identified three combinations that restored repair. The data suggest that: (i) defective repair is associated with colorectal and endometrial cancer and, by extrapolation, with other types of cancer; (ii) mutations in the hMSH2 gene, and possibly other genes, result in defective mismatch repair; (iii) the defect(s) in these lines likely involves pre-incision events or the excision step, but not the incision, polymerization, or ligation steps; and (iv) at least four functional complementation groups for mismatch repair may be involved in human cancer.

Relative probability of mutagenic translesion synthesis on the leading and lagging strands during replication of UV-irradiated DNA in a human cell extract

We have previously demonstrated mutagenic bypass of pyrimidine dimers during SV40 origin-dependent replication of UV-irradiated DNA in human cell extracts [Thomas, D. C., & Kunkel, T. A. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 7744-7748]. Here we use two vectors having the origin of replication on opposite sides of a lacZ alpha reporter gene to examine the relative probability of mutagenic translesion synthesis on the leading and lagging strands. Although replication of both vectors is inhibited by UVB irradiation in a dose-dependent manner, the covalently closed DNA products of replication contain T4 endonuclease sensitive sites, indicating that bypass of cyclobutane pyrimidine dimers occurred. At fluences of 70 and 100 J/m2, the mutant frequencies obtained with both vectors are substantially higher than with control DNAs. Sequence analysis of mutants obtained with both vectors reveal three types of mutations at frequencies significantly above those obtained from replication of undamaged DNA. These are C-->T transitions, accounting for about two-thirds of the mutants, a small number of CC-->TT substitutions, and complex mutations. Comparing the distribution of C-->T substitutions in the two spectra permits an estimation of the probability of mutagenic translesion replication of the same sequence when replicated as the leading or lagging strand. The data suggest that the overall average UV-independent C-->T substitution probability per phenotypically detectable dipyrimidine site is the same during leading and lagging strand replication. However, statistically significant differences are observed when the distribution of C-->T substitutions is considered.(ABSTRACT TRUNCATED AT 250 WORDS)

Blue-green (450-nm) upconversion Tm(3+):YLF laser

We report an upconversion laser that is pumped by two colors-one red and one near infrared-and emits in the blue-green region.

Amino acid sequence of Salmonella typhimurium branched-chain amino acid aminotransferase

The complete amino acid sequence of the subunit of branched-chain amino acid aminotransferase (transaminase B, EC 2.6.1.42) of Salmonella typhimurium was determined. An Escherichia coli recombinant containing the ilvGEDAY gene cluster of Salmonella was used as the source of the hexameric enzyme. The peptide fragments used for sequencing were generated by treatment with trypsin, Staphylococcus aureus V8 protease, endoproteinase Lys-C, and cyanogen bromide. The enzyme subunit contains 308 residues and has a molecular weight of 33,920. To determine the coenzyme-binding site, the pyridoxal 5-phosphate containing enzyme was treated with tritiated sodium borohydride prior to trypsin digestion. Peptide map comparisons with an apoenzyme tryptic digest and monitoring radioactivity incorporation allowed identification of the pyridoxylated peptide, which was then isolated and sequenced. The coenzyme-binding site is the lysyl residue at position 159. The amino acid sequence of Salmonella transaminase B is 97.4% identical with that of Escherichia coli, differing in only eight amino acid positions. Sequence comparisons of transaminase B to other known aminotransferase sequences revealed limited sequence similarity (24-33%) when conserved amino acid substitutions are allowed and alignments were forced to occur on the coenzyme-binding site.

Induction of the alkylation-inducible aidB gene of Escherichia coli by anaerobiosis

Induction of the adaptive response to alkylation damage results in the expression of four genes arranged in three transcriptional units: the ada-alkB operon and the alkA and aidB genes. Adaptive-response induction requires the ada gene product and occurs when cells are treated with methylating agents. In previous studies we noted that aidB, but not alkA or ada-alkB, was induced in the absence of alkylation damage as cells were grown to stationary phase. In this note we present evidence that aidB is induced by anaerobiosis. Thus, aidB is subject to dual regulation by ada-dependent alkylation induction and ada-independent anaerobic induction.

Microwave Conductivity: A New Technique for Gas-Phase Pulse Radiolysis

A new technique involving a combination of microwave absorption techniques and pulse radiolysis has been used to monitor electron processes in irradiated gases. The thermal electron attachment rate constants of various halogen-containing molecules have been measured and compared with the available literature values. The adaption of this technique for the measurement of electron-ion recombination rate constants and thermalization times for these gases is discussed.

Escherichia coli gene induction by alkylation treatment

Searches for alkylation-inducible (aid) genes of Escherichia coli have been conducted by screening random fusions of the Mu-dl(ApR lac) phage for fusions showing increased beta-galactosidase activity after treatment with methylating agents, but not after treatments with UV-irradiation. In this report we describe gene fusions that are specifically induced by alkylation treatments. Nine new mutants are described, and their properties are compared with the five mutants described previously. The total of 14 fusion mutants map at five distinct genetic loci. They can be further subdivided on the basis of their induction by methyl methanesulfonate (MMS) and N-methyl-N' -nitro-N-nitrosoguanidine (MNNG). alkA, aidB and aidD are induced by both agents and appear to be regulated by ada. Neither aidC nor aidI is regulated by ada. Moreover, since aidC is induced only by MNNG and aidI is induced only by MMS, these two genes are likely to be individually regulated. Thus, there appear to be at least three different regulatory mechanisms controlling aid genes.

Induction of specific Escherichia coli genes by sublethal treatments with alkylating agents

Fusions of the lac operon to genes induced by treatment with sublethal levels of alkylating agents have been selected from random insertions of the Mu-dl(ApRlac) phage by screening for induction of beta-galactosidase activity in the presence of methyl methanesulfonate. Genetic analysis reveals that these fusions resulted from insertion of Mu-dl(ApRlac) into two regions of the chromosome. One region (aidA) is near his and, based on phenotypic effects, appears to represent insertion into the alkA gene. The other region (aidB) is in the 92.3- to 98-min region, which harbors no previously identified genes involved in repair of alkylation damage. The aidB fusions caused increased resistance to alkylating agents and caused little or no change in the biological effects of adaptation to alkylating agents. Unlike the aidA fusions, aidB fusions showed increased beta-galactosidase activity in untreated cells in a growth phase-dependent fashion. The ada-5 mutation, which blocks expression of the adaptive response, decreased induction of beta-galactosidase activity in both aidA and aidB fusions after alkylation treatments. Thus, both aidA and aidB share with adaptive response a common regulatory mechanism involving the ada gene. The growth phase-dependent control of the aidB fusions, however, is unaffected by ada, suggesting that a second regulatory mechanism exists that controls only aidB.