An RNA foldability metric; implications for the design of rapidly foldable RNA sequences

Evidence is presented suggesting, for the first time, that the protein foldability metric σ = (T_θ − T_f) / T_θ, where T_θ and T_f are, respectively, the collapse and folding transition temperatures, could be used also to measure the foldability of RNA sequences. These results provide further evidence of similarities between the folding energy landscapes of proteins and RNA. The importance of σ is discussed in the context of the in silico design of rapidly foldable RNA sequences.     

Influence of the spacer length on the activity of enzymes immobilised on nylon/polyGMA membranes: Part 2: Non-isothermal conditions

β-Galactosidase has been immobilised through spacers of different length on nylon membranes grafted with glycidyl methacrylate. Hexamethylendiamine, ethylendiamine or hydrazine have been separately used as spacers.

The behaviour of the catalytic membranes has been studied in a bioreactor operating under non-isothermal conditions as a function of the applied temperature difference ΔT.

Comparison of the enzyme reaction rates under isothermal and non-isothermal conditions resulted in percentage activity increases (PAI) and reduction of the production time (τ_r) proportional to the size of the applied ΔT. Both these parameters increased with the increase of the spacer length.

Results have been discussed in the frame of reference of the process of thermodialysis which reduces the limitations to the diffusion of substrate and reaction products across the catalytic membrane, limitations introduced by the grafting and immobilisation process.

The advantages of employing non-isothermal bioreactors in biotechnological productive processes have been outlined.     

How are neuronal thermosensitivity and lack of thermoreception related in the duck's hypothalamus? A tentative answer

1. 1.|In 15 conscious Pekin ducks, 40 “warm sensitive” hypothalamic neurons were identified according to their discharge rates at 40°C T_hy (F₄₀), local temperature coefficients (Δ/ΔT) and Q₁₀.

2. 2.|Q₁₀ and either F₄₀ or ΔF/ΔT were little or not related.

3. 3.|A positive correlation between F₄₀ and ΔF/ΔT was observed which was particularly close (r = 0.94 and 0.96) when the neurons were classified according to their Q₁₀ of <2 and >2.

4. 4.|The results suggest that neurons with positive temperature coefficients in the duck's hypothalamus mostly exhibit linear to exponential temperature-discharge relationships.

5. 5.|This is an contrast to observations on mammalian hypothalamic thermosensitive neurons and may relate to the absence of the thermosensory function in the duck's rostral brainstem.

Evidence for modulation of cell-to-cell electrical coupling by cAMP in mouse islets of Langerhans

The effects of forskolin on electrical coupling among pancreatic β-cells were studied. Two microelectrodes were used to measure membrane potentials simultaneously in pairs of islet β-cells. Intracellular injection of a current pulse (ΔI) elicited a membrane response ΔV₁ in the injected cell and also a response ΔV₂ in a nearby β-cell confirming the existence of cell-to-cell electrical coupling among islet β-cells. In the presence of glucose (7 mM), application of forskolin evoked a transient depolarization of the membrane and electrical activity suggesting that the drug induced a partial inhibition of the β-cell membrane K⁺ conductance. Concomitant with this depolarization of the membrane there was a marked decrease in β-cell input resistance (ΔV₂/ΔI) suggesting that exposure to forskolin enhanced intercellular coupling. Direct measurements of the coupling ratio ΔV₂/ΔV₁ provided further support to the idea that forskolin enhances electrical coupling among islet cells. Indeed, application of forskolin reversibly increased the coupling ratio. These results suggest that cAMP might be involved in the modulation of electrical coupling among islet β-cells.     

Charophyte growth in small temperate water bodies: Extreme isotopic disequilibrium and implications for the palaeoecology of shallow marl lakes

A small pond containing the charophyte Chara hispida was monitored over a one-year period for changes in growth, water chemistry, water level and stable isotopic composition. Chara growth was found to be seasonal, with maximum growth occurring from late April to July. During this period, pH rose to > 10 while the dissolved inorganic carbon (DIC) and calcium fell as a result of photosynthesis and calcification. Large gradients in pH, water temperature and irradiance were found within the Chara sward and measurements showed that most growth and photosynthesis occurred within the upper 20 cm of the water column. Chara oospore formation was also found to be seasonal but dependent upon environmental conditions.

δ¹⁸O_w rose rapidly during summer as evaporation progressed and this was correlated with the δ¹⁸O_DIC, and to some extent with δ¹⁸O_c of the Chara encrusted calcite. However, extreme isotopic disequilibrium was observed between the δ¹⁸O_c and the δ¹⁸O_w and also between the δ¹³C_c and the δ¹³C_DIC. This arose from the high pH allowing atmospheric CO₂ to enter the water and combine directly with OH⁻.

It is concluded that, within shallow eutrophic lakes containing Chara swards, inferences of climate (e.g. air temperature) cannot be made from observations of the isotopic composition of Chara carbonates. However in combination with other geochemical data, disequilibrium events may be identifiable in ancient lake basins and taken as evidence for lake shallowing and/or eutrophication.     

Determination of the thermodynamics of carbonic anhydrase acid-unfolding by titration calorimetry

The enthalpy of unfolding (Δ_uH) of carbonic anhydrase II was determined by titrating the protein with acid and measuring the heat using isothermal titration calorimetry (ITC) in the temperature range of 5 to 59 °C. By combining the ITC results with our previous findings by differential scanning calorimetry (DSC) in the temperature range of 39 to 72 °C, the Δ_uH dependence over a wide temperature range was obtained. The temperature dependence of the enthalpy displays significant curvature indicating that the heat capacity of unfolding (Δ_uC_p) is dependent on temperature. The T-derivative of Δ_uC_p was equal to 100 ± 30 J/(mol × K²), with the result that the Δ_uC_p is equal to 15.8 kJ/(mol × K) at 5 °C, 19.0 kJ/(mol × K) at 37 °C and 21.8 kJ/(mol × K) at 64 °C. The enthalpy of unfolding is zero at 17 °C. At lower temperatures, the Δ_uH becomes exothermic.

This method of determining protein unfolding thermodynamics using acid-ITC, significantly widens the accessible T-range, provides direct estimate of the thermodynamic parameters at physiological temperature, and gives further insight into the third T-derivative of the Gibbs free energy of unfolding.     

The combined effects of ambient temperature and enforced sustained swimming activity on body temperatures of arctic charr (Salvelinus alpinus L.)

1. 1.|The difference between tissue temperatures and ambient water temperatures (ΔT) of the ectothermic Arctic charr (Salvelinus alpinus L.) ranged between 0.2 and 0.6°C.

2. 2.|For fish held at 5.7°C there were no significant differences in ΔT of exercising fish and those of controls.

3. 3.|By contrast, for fish held at 1.7°C sustained exercise led to a significant increase in ΔT of all body compartments compared with fish held in standing water (controls).

4. 4.|It is suggested that Arctic charr are capable of a limited control of metabolic heat exchange between body compartments and surrounding water when subjected to sustained exercise and ambient temperatures <2°C.

Influence of spent brewer’s yeast β-glucan on gelatinization and retrogradation of rice starch

The effects of β-glucan (BG) prepared from spent brewer’s yeast on gelatinization and retrogradation of rice starch (RS) were investigated as functions of mixing ratio and of storage time. Results of rapid visco-analysis (RVA) indicated that addition of BG increased the peak, breakdown, setback, and final viscosities, but decreased the pasting temperatures of the rice starch/β-glucan (RS/BG) mixtures. Differential scanning calorimetry (DSC) data demonstrated an increase in onset (T_o), peak (T_p), and conclusion (T_c) temperatures and a decrease in gelatinization enthalpy (ΔH₁) with increasing BG concentration. Storage of the mixed gels at 4 °C resulted in a decrease in T_o, T_p, T_c, and melting enthalpy (ΔH₂). The retrogradation ratio (ΔH₂/ΔH₁) and the phase transition temperature range (T_c − T_o) of the mixed gels increased with storage time, but this effect was reduced by the addition of BG. BG addition also slowed the syneresis of the mixed gels. Results of dynamic viscoelasticity measurement indicated that the addition of BG promoted RS retrogradation at the beginning and then retarded it during longer storage times. The added BG also retarded the development of gel hardness during refrigerated storage of the RS/BG mixed gels.     

Contribution of the heme propionate groups to the electron transfer and electrostatic properties of myoglobin

The role of the heme propionate groups in determining the electron transfer and electrostatic properties of myoglobin have been studied by thermodynamic, kinetic, and spectroscopic studies of horse heart myoglobin in which the heme propionate groups are esterified. Spectroelectrochemical analysis has established that the E_m,7 of dimethylester heme-substituted Mb (DME-Mb) (E_m,7 = 100.2(2) mV vs. NHE (Normal Hydrogen Electrode) (25 °C) is increased  40 mV relative to that of the native protein with ΔH° = −12.9(2) kcal/mol and ΔS° = −51.0(8) cal/mol/deg (pH 7.0, μ = 0.1 M (phosphate)). The second order rate constant for reduction of DME-metMb by Fe(EDTA)²⁻ is increased  > 400-fold relative to that for reduction of native metMb to a value of 1.34(2) × 10³ M⁻¹ s⁻¹ with ΔS^‡ = −13(1) cal/mol/deg and ΔH^‡ = 9.2(3) (pH 7.0, μ = 0.1 M (phosphate)). Analysis of the pH dependences of the reduction potential and rate constant for reduction by Fe(EDTA)²⁻ demonstrates that heme propionate esterification introduces significant changes into the electrostatic interactions in myoglobin. These changes are also manifested by differences in the pH dependences of the ¹H NMR spectra of native and DME-metMb that reveal shifts in pK_a values for specific His residues as the result of heme propionate esterification. In sum, the current results establish that heme propionate esterification not only affects the electron transfer properties of myoglobin but also influences the titration behavior of specific His residues.     

Pustulan and branched β-galactofuranan from the phytopathogenic fungus Guignardia citricarpa, excreted from media containing glucose and sucrose

Guignardia citricarpa is a phytopathogenic fungus and the causal agent of citrus black spot. Incubation in a semi-defined media resulted in formation of exopolysaccharides [EPS(s)]. A medium containing glucose gave rise to a (1→6)-linked β-glucan (200 kD), pustulan, which was characterized by NMR and methylation analysis. A sucrose-containing medium provided a homogalactan (376 kD) and methylation analysis showed nonreducing end- (20%), 6-O- (53%) and 5,6-di-O-substituted Galf units (27%). An HMQC spectrum of the homogalactan showed C-1/H-1 signals at δ 108.2/4.820, 108.3/4.820 and 107.1/5.079, corresponding to three types of β- -Galf units. A DEPT analysis showed inverted signals (CH₂) at δ 67.8 and 67.2, corresponding to 6-O-substituted β- -Galf units, whereas a C-5 signal at δ 77.0 suggests 5-O-substitution, confirming a novel structure for a β-galactofuranan.     

Thermal properties of corn gluten meal and its proteic components

Thermal properties of corn gluten meal (CGM) and of its extracted proteic components (zein and glutelin) at 0% moisture content, is studied by dynamic mechanical thermal analysis (DMTA) and modulated differential scanning calorimetry (MDSC). The glass transition temperature (T_g) on first heating, is measured at 176 and 174°C, respectively, for hot-air-dried and native CGM. For zein and glutelin isolated fractions, the measured T_g values are 164 and 209°C, respectively. The calculated T_g from using Matveev’s method (Matveev YI. Spec Publ R Soc Chem 1995;156;552) is in good agreement with experimental data for zein, a well defined protein. MDSC allows the measurement of change in heat capacity at T_g (ΔCp) with a single heating scan, avoiding sample alteration, and ΔCp values are 0.365 J/g per K for zein and 0.184 J/g per K for glutelin. The differences observed in T_g, relaxation temperatures, ΔCp and tan δ peak height are related to differences in the structure of the proteins, through the cross-linkages and hydrogen or van der Waals interactions. Experimental data from DMTA and MDSC, and the Couchman–Karasz thermodynamic approach indicate that CGM behaves as a miscible blend of its components, with high non-polar interactions between zein and glutelin proteins.     

A new floating sensor array to detect electric near fields of beating heart preparations

A new flexible sensor for in vitro experiments was developed to measure the surface potential, Φ, and its gradient, E (electric near field), at given sites of the heart. During depolarisation, E describes a vector loop from which direction and magnitude of local conduction velocity θ can be computed. Four recording silver electrodes (14 μm × 14 μm) separated by 50 μm, conducting leads, and solderable pads were patterned on a 50 μm thick polyimide film. The conductive structures, except the electrodes, were isolated with polyimide, and electrodes were chlorided. Spacer pillars mounted on the tip fulfil two functions: they keep the electrodes 70 μm from the tissue allowing non-contact recording of Φ and prevent lateral slipping. The low mass (9.1 mg) and flexibility (6.33 N/m) of the sensor let it easily follow the movement of the beating heart without notable displacement. We examined the electrodes on criteria like rms-noise of Φ, signal-to-noise ratio of Φ and E, maximum peak-slope recording dΦ/dt, and deviation of local activation time (LAT) from a common signal and obtained values of 24–28 μV, 46 and 41 dB, 497–561 V/s and no differences, respectively. With appropriate data acquisition (sampling rate 100 kHz, 24-bit), we were able to record Φ and to monitor E and θ on-line from beat-to-beat even at heart rates of 600 beats/min. Moreover, this technique can discriminate between uncoupled cardiac activations (as occur in fibrotic tissue) separated by less than 1 mm and 1 ms.     

Changes in denaturation and rheological properties of collagen-hyaluronic acid scaffolds as a result of temperature dependencies

This report describes the effect of temperature on the mechanical viscoelastic properties such as: storage modulus (E′), loss modulus (E″), and loss tangent (tan δ) of the collagen sponges modified with hyaluronic acid (HA). In order to detect collagen–HA copolymer denaturation and to assess its thermal stability, the differential scanning calorimetry (DSC) supplemented by thermogravimetric (TG) measurements was used. The denaturation temperature (T_d) of unmodified collagen samples increased from 69 to 86 °C for cross-linked samples, respectively. These temperature dependencies show remarkable changes in E′ and E″ at selected temperature up to 226 °C for all samples due to the release of loosely and strongly bound water. The influence of HA on the viscoelastic behavior of collagen is manifested by a shift of the tan δ peak associated with the process of decomposition towards higher temperatures resulting in a higher thermo-stability of the modified scaffolds.     

Anti-diabetic properties of the Canadian lowbush blueberry Vaccinium angustifolium Ait.

Incidence of type II diabetes is rapidly increasing worldwide. In order to identify complementary or alternative approaches to existing medications, we studied anti-diabetic properties of Vaccinium angustifolium Ait., a natural health product recommended for diabetes treatment in Canada. Ethanol extracts of root, stem, leaf, and fruit were tested at 12.5 μg/ml for anti-diabetic activity in peripheral tissues and pancreatic β cells using a variety of cell-based bioassays. Specifically, we assessed: (1) deoxyglucose uptake in differentiated C2C12 muscle cells and 3T3-L1 adipocytes; (2) glucose-stimulated insulin secretion (GSIS) in β TC-tet pancreatic β cells; (3) β cell proliferation in β TC-tet cells; (4) lipid accumulation in differentiating 3T3-L1 cells; (5) protection against glucose toxicity in PC12 cells. Root, stem, and leaf extracts significantly enhanced glucose transport in C2C12 cells by 15–25% in presence and absence of insulin after 20 h of incubation; no enhancement resulted from a 1 h exposure. In 3T3 cells, only the root and stem extracts enhanced uptake, and this effect was greater after 1 h than after 20 h; uptake was increased by up to 75% in absence of insulin. GSIS was potentiated by a small amount in growth-arrested β TC-tet cells incubated overnight with leaf or stem extract. However, fruit extracts were found to increase ³H-thymidine incorporation in replicating β TC-tet cells by 2.8-fold. Lipid accumulation in differentiating 3T3-L1 cells was accelerated by root, stem, and leaf extracts by as much as 6.5-fold by the end of a 6-day period. Stem, leaf, and fruit extracts reduced apoptosis by 20–33% in PC12 cells exposed to elevated glucose for 96 h. These results demonstrate that V. angustifolium contains active principles with insulin-like and glitazone-like properties, while conferring protection against glucose toxicity. Enhancement of proliferation in β cells may represent another potential anti-diabetic property. Extracts of the Canadian blueberry thus show promise for use as a complementary anti-diabetic therapy.     

Examination of an Oligocene lacustrine ecosystem using C and N stable isotopes

The Late Oligocene (25.8 Ma) Enspel Fossillagerstätte in Westerwald, Germany, contains a comprehensive fossil ecosystem preserved with specimens retaining morphological detail and a concentration of organic material. Stable carbon and nitrogen isotope analyses were used to examine the lacustrine ecosystem preserved in one stratigraphic horizon. These data suggest the presence of several trophic levels, including primary producers (diatoms and higher plants), primary consumers (e.g., tadpoles and insects), and secondary consumers (e.g., the fish species Paleorutilus enspelensis). Terrigenous and aquatic plants were associated with the lowest δ¹³C and δ¹⁵N values (mean plant = − 26.28‰ ± 0.45, 3.18‰ ± 1.04), primary consumers such as flies are one trophic level higher, and carnivores such as fish are yet another level higher. The δ¹⁵N values for P. enspelensis also showed enrichment in ¹⁵N with increasing body length, implying a shift in diet or feeding strategy with size. P. enspelensis and tadpole (Pelobates decheni) samples showed intraorganism fractionation between ‘muscle’ and ‘bone’ tissues. Stable carbon and nitrogen isotope data from the measurement of components (shale, leaves and seeds) common to a number of different stratigraphic horizons showed significant variation between horizons. A number of the features of the stable isotopic data are similar to those relationships seen in modern ecosystems and therefore suggest that stable isotope analyses can contribute to understanding ancient ecosystems.     

Stable isotopic variations in modern herbivore tooth enamel, plants and water on the Tibetan Plateau: Implications for paleoclimate and paleoelevation reconstructions

Stable isotope analyses of fossil teeth and other authigenic minerals have been used to reconstruct the paleoenvironment and paleoelevation of the Tibetan Plateau. The accuracy of such reconstructions is limited by the lack of a comprehensive modern comparative database from the region. We analyzed the carbon and oxygen isotopic compositions (δ¹³C and δ¹⁸O values) of tooth enamel from modern herbivores, the δ¹³C values of grasses and the δ¹⁸O values of water samples collected from various elevations within the Tibetan Plateau to examine their relationships with modern environment/elevation. The δ¹³C values of enamel samples from horses, yaks and goats display a narrow range of variation, with a mean of − 10.7 ± 1.4‰ (n = 301), indicating that these modern herbivores were feeding predominantly on C3 plants, consistent with the current dominance of C3 vegetation in the region. Some of the samples have δ¹³C values between − 7.3 and − 10‰. Although these higher δ¹³C values could suggest consumption of some C4 plants by the animals, the lack of significant seasonal δ¹³C variations within individual teeth indicates that these higher enamel δ¹³C values are due to consumption of C3 plants experiencing water stress and/or some CAM plants rather than C4 plants. Our data show that the conservative “cut-off” δ¹³C value for a pure C3 diet within the Tibetan Plateau should be − 8‰ for modern herbivores and − 7‰ (or even − 6.5‰) for fossils if the region was as arid in the past as today. In contrast to the small intra-tooth δ¹³C variations within individual teeth, serial enamel samples display large intra-tooth δ¹⁸O variations, reflecting seasonal variations in the δ¹⁸O of meteoric water. The mean δ¹⁸O values of tooth enamel from yaks and horses show a strong correlation with water δ¹⁸O values, confirming that the δ¹⁸O of tooth enamel from obligate drinker generally tracks the δ¹⁸O of meteoric water. Unfortunately, elevation alone cannot explain most of the variance in the δ¹⁸O of precipitation and tooth enamel, suggesting that quantitative reconstruction of the paleoelevation of the Tibetan Plateau using re-constructed δ¹⁸O values of paleo-meteoric water from fossil enamel or other oxygen-bearing minerals is not warranted. For a given environment, horses have the lowest enamel–δ¹⁸O values while goats display the highest enamel–δ¹⁸O values among the species studied. The large inter-species δ¹⁸O variations are likely due to differences in physiology and diet/drinking behavior of the animals. This underscores the importance of species-specific studies when interpreting δ¹⁸O data of fossil mammalian teeth in a stratigraphic sequence as a record of paleoclimate changes.     

Characterisation of the beta-tubulin gene of Cylicocyclus nassatus?

mRNA and genomic DNA were isolated from adult Cylicocyclus nassatus, and the mRNA was reverse transcribed. The cDNA was PCR amplified using degenerate primers designed according to the alignment of the β-tubulin amino acid sequences of other species. To complete the coding sequence, the 3′ end was amplified with the 3′-RACE, and for amplification of the 5′ end the SL1-primer was used. The cDNA of the β-tubulin gene of C. nassatus spans 1429 bp and encodes a protein of 448 amino acids. Specific primers were developed from the cDNA sequence to amplify the genomic DNA sequence and to analyse the genomic organisation of the β-tubulin gene. The complete sequence of the genomic DNA of the β-tubulin gene of C. nassatus has a size of 2652 bp and is organised into nine exons and eight introns. The identities with the exons of the gru-1 β-tubulin gene of Haemonchus contortus range between 79% and 97%.     

Transformation of steroids by Bacillus strains isolated from the foregut of water beetles (Coleoptera:Dytiscidae): I. Metabolism of androst-4-en-3,17-dione (AD)

Two Bacillus strains were isolated from the foregut of the water beetle Agabus affinis (Payk.) and tested for their steroid transforming ability. After incubation with androst-4-en-3,17-dione (AD), 13 different transformation products were detected. AD was hydroxylated at C₆, C₇, C₁₁ and C₁₄, resulting in formation of 6β-, 7-, 11- and 14-hydroxy-AD. One strain also produced small amounts of 6β,14-dihydroxy-AD. Partly, the 6β-hydroxy group was further oxidized to the corresponding 6-oxo steroids. In addition, a specific reduction of the Δ⁴-double bond was observed, leading to the formation of 5-androstane derivatives. In minor yields the carbonyl functions at C₃ and C₁₇ were reduced leading to the formation of 3ξ-OH or 17β-OH steroids. EI mass spectra of the trimethylsilyl and O-methyloxime trimethylsilyl ether derivatives of some transformation products are presented for the first time.     

Evidence that Early Carboniferous ostracods colonised coastal flood plain brackish water environments

A study of the stable isotope composition (δ¹⁸O, δ¹³C) of biogenic (ostracod, mollusc) and authigenic carbonates in the Ballagan Formation, Lower Carboniferous of Scotland, coupled with evidence from sedimentology and associated fossil fauna and flora, supports the argument that this formation was deposited in a coastal flood plain setting, in brackish (0.5 < 30‰ NaCl) and hypersaline (> 40‰ NaCl) waters, but in the absence of persistent normal marine conditions. The oxygen isotope data from the Ballagan Formation divide into three clusters: a diagenetic field defined by low δ¹⁸O (< − 11‰ VPDB); an intermediary field (δ¹⁸O − 11‰ to − 9‰) composed of a mixture of known primary and secondary (diagenetic) carbonates; and samples within the range of − 9‰ to − 4‰ which, as far as we can ascertain, are largely unaltered. No samples give typical Early Carboniferous δ¹⁸O marine values. Average marine carbonates from Europe have δ¹⁸O between − 4‰ to − 3‰. The Ballagan Formation carbonates were probably deposited in evaporated freshwater and/or brackish water. This conclusion is supported by the presence of evaporites (gypsum, anhydrite, halite pseudomorphs) and common desiccation-cracked mudstone surfaces throughout the Ballagan Formation, suggesting conditions of fluctuating salinity in ephemeral bodies of water. The stable isotope data support the notion that the ostracod assemblages of the Ballagan Formation were colonising brackish water and hypersaline ecologies on a coastal flood plain during the Early Carboniferous, a stage of development that may have encouraged their colonisation of fully non-marine (limnetic) environments during the later Carboniferous. The ostracods include cytherellacean and kloedenellacean species known from marginal marine sites elsewhere, but probably tolerant of brackish water, podocopid species such as ‘Bythocypris’ aequalis that may have been adapted for brackish water settings on coastal flood plains (ephemeral lakes and lagoons), and paraparchitacean-dominated assemblages that may signal harsh (hypersaline or desiccating) environments.     

Influence of DNA repair on mutation spectra in Salmonella

This paper reviews the influence of DNA repair on spontaneous and mutagen-induced mutation spectra at the base-substitution (hisG46) and -1 frameshift (hisD3052) alleles present in strains of the Salmonella (Ames) mutagenicity assay. At the frameshift allele (mostly a CGCGCGCG target), ΔuvrB influences the frequency of spontaneous hotspot mutations (−CG), duplications, and deletions, and it also shifts the sites of deletions and duplications. Cells with pKM101+ΔuvrB spontaneously produce complex frameshifts (frameshifts with an adjacent base substitution). The spontaneous frequency of 1-base insertions or concerted (templated) mutations is unaffected by DNA repair, and neither mutation is inducible by mutagens. Glu-P-1, 1-nitropyrene (1NP), and 2-acetylaminofluorene (2AAF) induce only hotspot mutations and are unaffected by pKM101, whereas benzo(a)pyrene and 4-aminobiphenyl induce only hotspot in pKM101⁻, and hotspot plus complex in pKM101⁺. At the base-substitution allele (mostly a CC/GG target), the ΔuvrB allele increases spontaneous transitions in the absence of pKM101 and increases transversions in its presence. The frequency of suppressor mutations is decreased 4× by ΔuvrB, but increased 7.5× by pKM101. Both repair factors cause a shift in the proportion of mutations to the second position of the CC/GG target. With UV light and γ-rays, the ΔuvrB allele increases the proportion of transitions relative to transversions. pKM101 is required for mutagenesis by Glu-P-1 and 4-AB, and the types and positions of the substitutions are not altered by the addition of the ΔuvrB allele. Changes in DNA repair appear to cause more changes in spontaneous than in mutagen-induced mutation spectra at both alleles. There is a high correlation (r²=0.8) between a mutagen's ability to induce complex frameshifts and its relative base-substitution/frameshift mutagenic potency. A mutagen induces the same primary class of base substitution in TA100 (ΔuvrB, pKM101) as it does in Escherichia coli, mammalian cells, or rodents as well as in the p53 gene of human tumors associated with exposure to that mutagen. Thus, a mutagen induces the same primary class of base substitution in most organisms, reflecting the conserved nature of DNA replication and repair processes.