Novel Use for the Osmolyte Trimethylamine N-oxide: Retaining the Psychrophilic Characters of Cold-Adapted Protease Deseasin MCP-01 and Simultaneously Improving its Thermostability

The low thermostability of cold-adapted enzymes is a main barrier for their application. A simple and reliable method to improve both the stability and the activity of cold-adapted enzymes is still rare. As a protein stabilizer, the effect of trimethylamine N-oxide (TMAO) on a cold-adapted enzyme or protein has not been reported. In this study, effects of TMAO on the structure, activity, and stability of a cold-adapted protease, deseasin MCP-01, were studied. Deseasin MCP-01 is a new type of subtilase from deep-sea psychrotolerant bacterium Pseudoalteromonas sp. SM9913. Fluorescence and CD spectra showed that TMAO did not perturb the structure of MCP-01 and therefore kept the conformational flexibility of MCP-01. One molar TMAO improved the activity of MCP-01 by 174% and its catalytic efficiency (k _cat /K _m) by 290% at 0°C. In the presence of 1 M TMAO, the thermostability (t _1/2) of MCP-01 increased by two- to fivefold at 60∼40°C. Structural analysis with CD showed that 1 M TMAO could keep the structural thermostability of MCP-01 close to that of its mesophilic counterpart subtilisin Carlsberg when incubated at 40°C for 1 h. Moreover, 1 M TMAO increased the melting temperature (T _m) of MCP-01 by 10.5°C. These results suggest that TMAO can be used as a perfect stabilizing agent to retain the psychrophilic characters of a cold-adapted enzyme and simultaneously improve its thermostability.     

Reaction Products from Various Tocopherols with Trimethylamine Oxide and Their Antioxidative Activities

The structures of many reaction products obtained when various tocopherols (Toc’s) and trimethylamine oxide (TMAO) were treated in liquid paraffin under a nitrogen stream at 180°C, were determined and their antioxidative activities were investigated.

The reaction products (Toc dimers) isolated were as follows: α-tocopheryl ethane from α-Toc; 5-(γ-tocopheryloxy)-γ-Toc, 5-(γ-tocopheryl)-γ-Toc (two kinds) and α-tocopheryl ethane from γ-Toc; 5-(δ-tocopheryloxy)-δ-Toc from δ-Toc.

The two 5-(γ-tocopheryl)-γ-Toc’s are atropisomers of each other (TLC (Rf): 0.75, 0.45—benzene) and isomerization occurred within 20 min when they were treated under nitrogen at 180°C.

All Toc dimers, in particular 5-(γ-tocopheryloxy)-γ-Toc, have antioxidative activities and excellent synergism with TMAO in inhibiting the oxidation of lard kept in the dark at 60°C.     

Aflatoxin and Ochratoxin Production by <Emphasis Type="Italic">Aspergillus</Emphasis> Species Under Ex Vivo Conditions

Aspergillus species are increasingly important human pathogens. It is not known whether toxic metabolites of many of these pathogenic species can act as virulence factors in aspergillosis. We examined isolates of aflatoxin and ochratoxin-producing species for toxin production in ex vivo conditions. Seven of the 21 aflatoxin-producing isolates screened produced aflatoxin at 35 and 37°C on the general medium yeast extract sucrose agar (YES). However, none of them produced toxin at these temperatures on brain heart infusion agar (BHA), a medium that mimics human tissue, or on BHA with modified pH or sugar levels. Six of the 12 ochratoxin-producing isolates examined produced toxin at 35°C on YES. All three isolates of A. alliaceus produced ochratoxin on BHA or modified BHA at 37°C. One strain of A. pseudoelegans produced a minute amount of ochratoxin on modified BHA at 37°C. These data indicate that aflatoxin is an unlikely virulence, factor but that ochratoxin may be a potential virulence factor in aspergillosis.     

Untenability of the Heteronomous DNA Model for Poly(dA) · Poly(dT) in Solution. This DNA Adopts a Right-Handed B-DNA Duplex in Which the Two Strands are Conformationally Equivalent. A 500 MHz NMR Study Using One Dimensional NOE

Abstract

ID NOE ¹H NMR spectroscopy at 500 MHz was employed to examine the structure of poly(dA)·poly(dT) in solution. NOE experiments were conducted as a function of presaturation pulse length (50, 30, 20 and 10 msec) and.power (19 and 20 db) to distinguish the primary NOEs from spin diffusion. The 10 msec NOE experiments took 49 hrs and over 55,000 scans for each case and the difference spectra were almost free from diffusion.

The spin diffused NOE difference spectra as well as difference NOE spectra in 90% H₂O + 10% D₂O in which TNH3 was presaturated enabled to make a complete assignment of the base and sugar protons. It is shown that poly(dA) ·poly(dT) melts in a fashion in which single stranded bubbles are formed with increasing temperature.

Extremely strong primary NOEs were observed at H2′/H2″ when AH8 and TH6 were presaturated. The observed NOEs at AH2′ and that AH2″ were very similar as were the NOEs at TH2′ and TH2″. The observed NOEs at AH2′ and AH2″when AH8 was presaturated were very similar to those observed at TH2′ and TH2″ when TH6 was presaturated. In addition, presaturation of H1′ of A and T residues resulted in similar NOEs at AH2′/H2″ and TH2′/H2″ region and these NOEs at H2′ and H2″ were distinctly asymmetric as expected in a C2′-endo sugar pucker. There was not a trace of NOE at AH8 and TH6 when AH3′ and TH3′ were presaturated indicating that C3′-endo, × = 30–40° conformation is not valid for this DNA. From these NOE data, chemical shift shielding calculations and stereochemistry based computer modellings, we conclude that poly(dA)·poly(dT) in solution adopts a right- handed B-DNA duplex in which both dA and dT strands are conformationally equivalent with C2′-endo sugar pucker and a glycosyl torsion, ×, of ?73°, the remaining backbone torsion angles being φ′ = 221°, ω′ = 212°, ω = 310°, φ = 149°, ψ = 42°, ψ′ = 139°. The experimental data are in total disagreement with the heteronomous DNA model of Arnott et. al. proposed for the fibrous state. (Arnott, S., Chandrasekaran, R., Hall, I.H., and Puigjaner, L.C., Nucl. Acid Res. 11, 4141, 1983).     

The effect of temperature on the bacterial load and microbial composition in Norway lobster (Nephrops norvegicus) tail meat during storage

Aims: The aim of this study was to update and extend our knowledge of the bacterial load and microbial composition in Norway lobster (Nephrops norvegicus) under commercially relevant storage conditions to optimize handling procedures. Methods and Results: Total viable counts were performed at different storage temperatures (0, 4, 8, 10, 12 or 16°C) and after different storage times (1–7 days). Storage at 16°C was found to be most detrimental, and storage at 0°C was found to be optimal. 16S‐rRNA sequencing was utilized to determine the composition of the bacteria within the microflora. In this way, Photobacterium isolates, especially Photobacterium phosphoreum, were identified as the main specific spoilage organisms. The abilities to reduce trimethylamineoxide (TMAO) and to produce H₂S were analysed in a selection of bacterial isolates. The higher the incubation temperature during storage, the more isolates were found to reduce TMAO and produce H₂S. Conclusions: Nephrops norvegicus possesses an unusually high initial microbial load when fresh. Storage temperature is the most crucial factor affecting microbial growth, microbial activity and spoilage potential in N. norvegicus produce. Spoilage can be attributed mainly to P. phosphoreum. Significance and Impact of the Study: This study presents significant new findings with regard to the progression and causative agents of spoilage in N. norvegicus. Based on the results, we can recommend that N. norvegicus tails should be stored in a 0°C environment immediately after catch. Stored this way, the growth and spoilage activity of the microflora may be reduced significantly and an extension of shelf life might be attained.     

Enhancement of Polyunsaturated Fatty Acid Production by Tn5 Transposon in Shewanella baltica

Transposon Tn5 mutagenesis was used to generate random mutations in Shewanella baltica MAC1, a polyunsaturated fatty acid (PUFA)-producing bacterium. Three mutants produced 3–5 times more eicosapentaenoic acid (EPA 20:5 n−3) compared to the wild type at 10°C. One of the mutants produced 0.3 mg EPA g⁻¹ when grown at high temperature (30°C). Moreover, 2 mg docosahexaenoic acid (DHA 22:6 n−3) g⁻¹ was produced by S. baltica mutants at 4°C. Sequencing of insertion mutation(s) showed 96% homology to trimethylamine N-oxide (TMAO) reductase gene and 85% homology to rRNA operons of E. coli. Tn5 transposon mutagenesis therefore is a suitable technique to increase PUFA formation in bacteria.     

Crystal structure of guanylyl-2′,5′-cytidine dihydrate: An analogue of msDNA-RNA junction in stigmatella aurantiaca

Sequence analysis of msDNA from bacterium such as Stigmatella aurantiaca, Myxococcus xanthus and Escherichia coli B revealed that the guanine residue of the single-stranded RNA is linked to the cytosine residue of the msDNA through a 2′–5′ instead of a conventional 3′–5′ phosphodiester bond. We have now obtained the crystal structure of the self-complementary dimer guanylyl-2′,5′-cytidine (G2′p5′C) that occurs at the msDNA-RNA junction. G2′p5′C crystallizes in the orthorhombic space group P2₁2₁2₁ with a = 8.376(2), b = 16.231(5), c = 18.671(4). CuK ∝ intensity data were collected on a diffractometer in the ω ?2θ scan mode. The amount of 1699 out of 2354 reflections having I ≥ 3σ (F) were considered observed. The structure was solved by direct methods and refined by full-matrix least squares to a R factor of 0.054. The conformation of the guanine base about the glycosyl bond is syn (χ₁ = ?54°) and that of cytosine is anti (χ₂ = 156°). The 5′ and 2′ and ribose moieties show C2′-endo and C3-endo mixed puckering just like in A2′p5′A, A2′p5′C, A2′p5U, and dC3′p5′G. Charge neutralization in G2′p5′C is accomplished through protonation of the cytosine base. An important feature of G2′p5′C is the stacking of guanine on ribose 04′ of cytosine similar to that seen in other 2′–5′ dimers. G2′p5′C, unlike its 3′–5′ isomer, does not form a miniature double helix with the Watson-Crick base-pairing pattern. Comparison of G2′p5′C with A2′p5′C reveals that they are isostructural. A branched trinucleotide model for the msDNA-RNA junction has been postulated. © 1994 John Wiley & Sons, Inc.     

Structure of guanylyl-3',5'-cytidine monophosphate. II. Description of the molecular and crystal structure of the calcium derivative in space group P2(1).

The structural features of calcium guanosine-3′,5′-cytidine monophosphate (GpC) have been elucidated by X-ray diffraction analysis. The molecule was crystallized in space group P2₁ with cell constants of a = 21.224 Å, b = 34.207 Å, c = 9.327 Å, and β = 90.527°, Z = 8. The hydration of the crystal is 21% by weight with 72 water molecules in the unit cell. The four GpC molecules in the asymmetric unit occur as two Watson-Crick hydrogen-bonded dimers related by a pseudo-C face centering. Each dimer consists of two independent GpC molecules whose bases are hydrogen bonded to each other in the traditional Watson-Crick fashion. Each dimer possesses a pseudo twofold axis broken by a calcium ion and associated solvent. The four molecules are conformationally similar to helical RNA, but are not identical to it or to each other. Instead, values of conformational angles reflect the intrinsic flexibility of the molecule within the range of basic helical conformations. All eight bases are anti, sugars are all C3′-endo, and the C4′-C5′ bond rotations are gauche-gauche. The R factor is 12.6% for 2918 observed reflections at 1.2-Å resolution.     

Tridec-1-ene-3,5,7,9,11-pentayne,an Ovicidal Substance from Xanthium canadense

Pyridoxamine (pyridoxine) 5′-phosphate oxidase (EC. 1.4.3.5) has been purified from dry baker’s yeast to an apparent homogeneity on a polyacrylamide disc gel electrophoresis in the presence of 10 µm of phenylmethylsulfonyl fluoride throughout purification.

1) The purified enzyme, obtained as holo-flavoprotein, has a specific activity of 27µmol/mg/hr for pyridoxamine 5′-phosphate at 37°C, and a ratio of pyridoxine 5′-phosphate oxidase to pyridoxamine 5′-phosphate oxidase is approximately 0.25 at a substrate concentration of 285 µm. Km values for both substrates are 18 µm for pyridoxamine 5′-phosphate and 2.7 µm for pyridoxine 5′-phosphate, respectively.

2) The enzyme can easily oxidize pyridoxamine 5′-phosphate, but when pyridoxamine and pyridoxine 5′-phosphate are coexisted in a reaction mixture the enzyme activity is markedly suppressed much beyond the values expected from its high affinity (low Km) and low V_max for the latter substrate.

3) Optimum temperature for both substrates is approximately 45°C, and optimum pH is near 9 for pyridoxamine 5′-phosphate and 8 for pyridoxine 5′-phosphate.

4) From the data obtained, the mechanism of regulation of this enzyme in production of pyridoxal 5′-phosphate and a reasonable substrate for the enzyme in vivo are discussed.     

Effect of photoperiod and temperature on apical growth cessation in two ecotypes of Salix and Betula

Apical growth cessation as affected by photoperiod and temperature has been studied in seedlings of two latitudinal ecotypes of Salix and Betula. The critical photoperiod for apical growth cessation at constant temperatures of 15 and 21°C was about 22 h for a northern (69°C39′N) and about 15–16 h for a southern (59°C40′N) ecotype of Salix pentandra. Fluctuating day/night temperatures (21°C/9°C, 15°C/6°C) induced apical growth cessation in northern ecotypes even at 24–h photoperiod. Disagreements in critical photoperiods found in various studies are discussed.     

Conformational analysis of the 2'-deoxyribofuranose ring from proton-proton coupling constants: analysis of a nucleoside-carcinogen adduct formed from 2-acetylaminofluorene utilizing a three-state model

The conformation of the sugar moiety of 8-(N-fluoren-2-ylamino)-2′-deoxyguanosine in solution has been examined as a function of temperature by ¹H-nmr spectroscopy. Analysis of coupling constants shows that lowering the temperature to ?50°C in methanol shifts the conformational equilibrium of the sugar ring resulting in a C2′-endo conformation at a mole fraction of 0.97. The computed phase angle of pseudorotation and amplitude of pucker are 154° and 36°, respectively, with very little discrepancy between the five calculated coupling constants and coupling constants extrapolated from the temperature profiles. A computer program has been written enabling a three-state best-fit analysis. The three-state analysis indicates an equilibrium between C2′-endo, C3′-endo, and 04′-endo conformations. In aqueous solution, the computed mole fraction of the 04′-endo form is 0.18 at 30°C. The conformation associated with the sugar ring and the C4′? C5′ bond is compared to that of 2′-deoxyguanosine.     

Geographic variation in photoperiodic diapause induction and diapause intensity in Sericinus montelus (Lepidoptera: Papilionidae)

Abstract Due to the risk of extinction and ornamental value of the swallowtail butterfly, Sericinus montelus Gray (Lepidoptera: Papilionidae) in China, knowledge about local adaptations is important for the conservation and economical utilization of the species. In the present study, photoperiodic diapause induction and diapause intensity of S. montelus populations from Jiamusi (46°37′N), Beijing (40°15′N), Zibo (36°48′N), Fangxian (32°36′N), Wuhan (30°33′N) and Huaihua (27°33′N) were characterized at 25°C. Logistic regression analysis revealed a significant population × hours of light interaction, confirming that photoperiodic responses varied among populations. The critical photoperiod was positively correlated with latitude and increased toward the north at a rate of about 1 h for each 6.67 degrees of latitude. Survival analyses indicated that survival time of diapausing pupae before adult eclosion differed significantly among populations at 25°C and 16 : 8 L : D h. The mean duration of pupal diapause was also positively correlated with latitude. Our study reveals geographic variation in the critical photoperiod for diapause induction and in diapause intensity of S. montelus. These results provide useful information for our general understanding about seasonal adaptation in insects and may also be used to predict how geographic populations respond to climate warming.     

Intersubunit Disulfide Interactions Play a Critical Role in Maintaining the Thermostability of Glucose-6-phosphate Dehydrogenase from the Hyperthermophilic Bacterium Aquifex aeolicus

Proteins from thermophilic microorganisms are stabilized by various mechanisms to preserve their native folded states at higher temperatures. A thermostable glucose-6-phosphate dehydrogenase (tG6PDH) from the hyperthermophilic bacterium Aquifex aeolicus was expressed as a recombinant protein in Escherichia coli. The A. aeolicus G6PDH is a homodimer exhibiting remarkable thermostability (t_1/2=24 hr at 90°C). Based on homology modeling and upon comparison of its structure with human G6PDH, it was predicted that cysteine 184 of one subunit could form a disulfide bond with cysteine 352 of the other subunit resulting in reinforced intersubunit interactions that hold the dimer together. Site-directed mutagenesis was performed on tG6PDH to convert C184 and C352 to serines. The tG6PDH double mutant exhibited a dramatic decrease in the half-life from 24 hr to 3 hr at 90°C. The same decrease in half-life was also found when either C184 or C352 was mutated to serine. The result indicates that C184 and C352 may play a crucial role in strengthening the dimer interface through disulfide bond formation, thereby contributing to the thermal stability of the enzyme.     

Temperature adaptation of soil bacterial communities along an Antarctic climate gradient: predicting responses to climate warming

Soil microorganisms, the central drivers of terrestrial Antarctic ecosystems, are being confronted with increasing temperatures as parts of the continent experience considerable warming. Here we determined short‐term temperature dependencies of Antarctic soil bacterial community growth rates, using the leucine incorporation technique, in order to predict future changes in temperature sensitivity of resident soil bacterial communities. Soil samples were collected along a climate gradient consisting of locations on the Antarctic Peninsula (Anchorage Island, 67 °34′S, 68 °08′W), Signy Island (60 °43′S, 45 °38′W) and the Falkland Islands (51 °76′S 59 °03′W). At each location, experimental plots were subjected to warming by open top chambers (OTCs) and paired with control plots on vegetated and fell‐field habitats. The bacterial communities were adapted to the mean annual temperature of their environment, as shown by a significant correlation between the mean annual soil temperature and the minimum temperature for bacterial growth (T_min). Every 1 °C rise in soil temperature was estimated to increase T_min by 0.24–0.38 °C. The optimum temperature for bacterial growth varied less and did not have as clear a relationship with soil temperature. Temperature sensitivity, indicated by Q₁₀ values, increased with mean annual soil temperature, suggesting that bacterial communities from colder regions were less temperature sensitive than those from the warmer regions. The OTC warming (generally <1 °C temperature increases) over 3 years had no effects on temperature relationship of the soil bacterial community. We estimate that the predicted temperature increase of 2.6 °C for the Antarctic Peninsula would increase T_min by 0.6–1 °C and Q₁₀ (0–10 °C) by 0.5 units.     

Length‐weight and length–length relationships of three algae‐scraping cyprinid species from Iran

The study presents length–weight relationships (LWRs) and length–length relationships (LLRs) for three algae‐scraper species; Capoeta coadi from the Kouhrang River (Iran; 32°23′N, 50°08′E) a part of the Tigris drainage basin, Capoeta pyragyi from Cheshmeh Langan River (32°55′N, 50°10′E) a part of Zayanderud River basin and Capoeta umbla from Chooman River (35°57′N, 45°47′E). Fish were sampled by electro fishing (Samus1000; Power Out: 200 watts) in August, September and October 2017. Sampling was carried out each months in sites covering an area of about 100 m² including runs, riffles and pools at a water depth of 10–60 cm. The obtained LWRs and LLRs showed a high level of correlation (r² > 0.99).     

Proton magnetic resonance study of nucleosides,nucleotides, and dideoxynucleoside monophosphates containing a syn pyrimidine base

Proton magnetic resonance data have been obtained for 6-methyl-2′-deoxyuridine (dT*), its 3′- and 5′-monophosphates, and its 3′,5′-diphosphate, as well as for the corresponding thymine derivatives. The synthesis of the dideoxynucleoside monophosphates—d(TpT), d(T*pT), d(TpT*), and d(T*pT*)—was accomplished, and spectral data were obtained for these four dimers. The data show that the 6-methyluracil base prefers the syn conformation about the N-glycosyl bond at the monomer and dimer levels. The presence of the syn base leads to increases in the cis couplings of the sugar ring, J_1′2″ and J_2′3′, which indicate a trend towards eclipsing of the substituents on the C1′-C2′ and C2′-C3′ fragments. This trend is discussed in terms of changes in the pseudorotational parameters which describe the pucker of the ring. The syn base destabilizes the g⁺ conformer about the C4′-C5′ bond, leading to a preference for the t conformer in all dT* residues at the monomer and dimer levels. Preliminary work on the formation of cyclobutane-type photodimers in d(T*pT) and d(T*pT*) is discussed and presented as evidence for the capability of the syn 6-methyluracil base to form base-stacked complexes.     

Overexpression and characterization of dimeric and tetrameric forms of recombinant serine hydroxymethyltransferase from Bacillus stearothermophilus

Serine hydroxymethyltransferase (SHMT), a pyridoxal-5′-phosphate (PLP) dependent enzyme catalyzes the interconversion of L-Ser and Gly using tetrahydrofolate as a substrate. The gene encoding for SHMT was amplified by PCR from genomic DNA ofBacillus stearothermophilus and the PCR product was cloned and overexpressed inEscherichia coli. The purified recombinant enzyme was isolated as a mixture of dimer (90%) and tetramer (10%). This is the first report demonstrating the existence of SHMT as a dimer and tetramer in the same organism. The specific activities at 37°C of the dimeric and tetrameric forms were 6.7 U/mg and 4.1 U/mg, respectively. The purified dimer was extremely thermostable with aT _m of 85°C in the presence of PLP and L-Ser. The temperature optimum of the dimer was 80°C with a specific activity of 32.4 U/mg at this temperature. The enzyme catalyzed tetrahydrofolate-independent reactions at a slower rate compared to the tetrahydrofolate-dependent retro-aldol cleavage of L-Ser. The interaction with substrates and their analogues indicated that the orientation of PLP ring ofB. stearothermophilus SHMT was probably different from sheep liver cytosolic recombinant SHMT (scSHMT).     

The A and B conformations of DNA and RNA subunits. Potential energy calculations for dGpdC

In order to obtain a molecular picture of the A and B forms of a DNA subunit, potential energy calculations have been made for dGpdC with C(3′)-endo and C(2′)-endo [or C(3′)-exo] sugar puckerings. These are compared with results for GpC. The global minima for dGpdC and GpC are almost identical. They are like A-form duplex DNA and RNA, respectively, with bases anti, the ω′, ω angle pair near 300°, 280°, and sugar pucker C(3′)-endo. For dGpdC, a B-form helical conformer, with sugar pucker C(2′)-endo and ω′ = 257°, ω = 298°, is found only 0.4 kcal/mol above the global minimum. A second low-energy conformation (2.3 kcal/mol) has ω′ = 263°, ω = 158° and ψ near 180°. This has dihedral angles like the original Watson–Crick model of the double helix. In contrast, for GpC, the C(2′)-endo B form is 6.9 kcal/mol above the global minimum. These theoretical results are consistent with experimental studies on DNA and RNA fibers. DNA fibers exist in both A and B forms, while RNA fibers generally assume only the A form. A low-energy conformation unlike the A or B forms was found for both dGpdC and GpC when the sugars were C(3′)-endo. This conformation—ω′,ω near 20°,80°—was not observed for C(2′)-endo dGpdC. Energy surface maps in the ω′,ω plane showed that C(2′)-endo dGpdC has one low-energy valley. It is in the B-form helical region (ω′ ～ 260°, ω ～ 300). When the sugar pucker is C(3′)-endo, dGpdC has two low-energy regions: the A-form helical region and the region with the minimum at ω′ = 16°, ω = 85°.     

Pathology and properties of tulip virus X, a new potexvirus

Tulip virus X (TVX), a previously undescribed mechanically transmissible virus, causes chlorotic and necrotic lesions in leaves and streaks of intensified pigmentation in tepals of tulip plants. The virus infected 22 of 42 other plant species in 10 of 14 families, but most host species were infected only erratically. TVX is best propagated in Chenopodium quinoa and assayed in C. amaranticolor. Spindleshaped inclusions were observed in epidermal cells of C. amaranticolor leaves. Leaf extracts from C. quinoa contained flexuous filamentous particles measuring c. 495 ×13 nm. The extracts were infective after dilution to 10^-9, after heating for 10 min at 60 °C but not at 65 °C, and after storage at c. 20 °C for 30 days or at -20 °C for 6 months. TVX particles were purified (500 μg/g C. quinoa leaf) from tissue extracts in 0.067 M phosphate buffer containing 10 mM EDTA at pH 7, by twice precipitating the virus with 8% polyethylene glycol in 0.2 M NaCl followed by differential centrifugation. The virus particles have a sedimentation coefficient (s_{20, w}) of 102 S. They contain a protein of mol. wt c. 22 500 and a nucleic acid that, when glyoxalated, migrates in agarose gel like single-stranded RNA of mol. wt 2.05 × 10⁶. TVX particles tend to aggregate, and evidence was obtained that a 118 S component which was consistently observed in purified preparations and in infective sap is an end-to-end dimer. A distant serological relationship was found between particles of TVX and those of viola mottle and hydrangea ringspot viruses, but no serological relationship was detected to nine other potexviruses. TVX is considered to be a distinct and definitive member of the potexvirus group.