Mechanism of How Salt-Gradient-Induced Charges Affect the Translocation of DNA Molecules through a Nanopore

Experiments using nanopores demonstrated that a salt gradient enhances the capture rate of DNA and reduces its translocation speed. These two effects can help to enable electrical DNA sequencing with nanopores. Here, we provide a quantitative theoretical evaluation that shows the positive net charges, which accumulate around the pore entrance due to the salt gradient, are responsible for the two observed effects: they reinforce the electric capture field, resulting in promoted molecule capture rate; and they induce cationic electroosmotic flow through the nanopore, thus significantly retarding the motion of the anionic DNA through the nanopore. Our multiphysical simulation results show that, during the polymer trapping stage, the former effect plays the major role, thus resulting in promoted DNA capture rate, while during the nanopore-penetrating stage the latter effect dominates and consequently reduces the DNA translocation speed significantly. Quantitative agreement with experimental results has been reached by further taking nanopore wall surface charges into account.     

Analysis of Slow Hyperpolarizing Potentials in Frog Taste Cells Induced by Glossopharyngeal Nerve Stimulation

Chemical Senses, 29,     

Physiological evaluation of temperature effect on the growth processes of the mysid, Neomysis intermedia Czerniawsky

Ingestion, respiration, and molting loss rates were measuredover the 3 – 29°C range in Neomysis intermedia. Weightspecific rates of these physiological processes ranged from2 to 140% body C day^–1 for ingestion, from 2 to 15% bodyC day^–1 for respiration, and from 0.1 to 5% body C day^–1for molting loss. All weight-specific rates showed a logarithmicdecrease with a logarithmic increase in body weight, and a logarithmicincrease with a linear increase in temperature below 20 or 25°C.The effect of temperature, however, was different between thephysiological rates, with a large temperature dependency foringestion (Q₁₀ = 2.6 –3.9) and molting loss (Q¹⁰ = 2.9– 3.6) and a moderate temperature dependency for respiration(Q₁₀ = 1.9 – 2.1). Calculated assimilation efficiencychanged with body size, but was constant over the temperaturerange examined. Allocation of assimilated materials varied witha change in temperature, reflecting the different temperaturedependence between physiological processes. It was deduced thatthe strong temperature dependency of the growth rate in N. intermediaobserved in the previous studies resulted from the large temperatureeffect on ingestion and assimilation rates, superimposed bythe different allocation of assimilated materials. ¹Present address: Department of Botany, University of Tokyo,Hongo, Tokyo 113, Japan     

Selective growth of a mutant in continuous culture of Bacillus caldolyticus for production of α-amylase

Summary In a continuous culture of Bacillus caldolyticus strain SP, which requires maltose as an inducer for production of -amylase in batch culture, a predominant mutant strain M1 which produced high amounts of -amylase in the absence of maltose in batch culture, developed. The change of cell population from strain SP to strain M1 in maltose-casitone medium was linear with time in the transient state after the change from batch to continuous culture at a dilution rate of 0.17 h^-1, and was completed in about 11 generations of bacterial growth. The dilution rate effect of continuous culture on -amylase activity was almost the same with both strains SP and M1. The maximum -amylase activity of 380 units/ml was observed at an intermediate dilution rate that was 11.5 times higher than -amylase activity at the end of a batch culture using the same medium. It was deduced that the enhancement of -amylase production in continuous culture was attributed partly to the predominant growth of a mutant strain with higher -amylase productivity.     

Isolation and Characterization of an Enterobacter cloacae Strain That Reduces Hexavalent Chromium under Anaerobic Conditions

An Enterobacter cloacae strain (HO1) capable of reducing hexavalent chromium (chromate) was isolated from activated sludge. This bacterium was resistant to chromate under both aerobic and anaerobic conditions. Only the anaerobic culture of the E. cloacae isolate showed chromate reduction. In the anaerobic culture, yellow turned white with chromate and the turbidity increased as the reduction proceeded, suggesting that insoluble chromium hydroxide was formed. E. cloacae is likely to utilize toxic chromate as an electron acceptor anaerobically because (i) the anaerobic growth of E. cloacae HO1 accompanied the decrease of toxic chromate in culture medium, (ii) the chromate-reducing activity was rapidly inhibited by oxygen, and (iii) the reduction occurred more rapidly in glycerol- or acetate-grown cells than in glucose-grown cells. The chromate reduction in E. cloacae HO1 was observed at pH 6.0 to 8.5 (optimum pH, 7.0) and at 10 to 40°C (optimum, 30°C).     

Cloning and sequence analysis of a cDNA encoding the Rieske iron-sulfur protein of rat mitochondrial cytochrome bc1 complex

We have isolated a cDNA clone for the Rieske iron-sulfur protein of rat cytochrome bc1 complex, by screening a rat liver cDNA expression library using antiserum directed against the corresponding protein of bovine. The amino acid sequence deduced from the nucleotide sequence of the cDNA indicated that the mature polypeptide of the rat protein consists of 196 amino acid residues with a molecular weight of 21,465, and that it is formed as a precursor with an amino-terminal extension. Northern blot analysis indicated that rat liver possibly contains different sizes of mRNAs for the Rieske iron-sulfur protein, and Southern blot analysis demonstrated that rats and mice possess a single gene for this protein.     

Cloning and sequencing of a cDNA for human mitochondrial ubiquinone-binding protein of complex III

The ubiquinone-binding protein (QP-C) is a nuclear-encoded component of ubiquinol-cytochrome c oxidoreductase in the mitochondrial respiratory chain and plays an important role in electron transfer as a ubiquinone-QP-C complex. We obtained a partial cDNA for rat liver QP-C by screening a lambda gt11 rat liver cDNA library using antiserum directed against bovine heart QP-C. Using this cDNA as a probe, a cDNA clone was isolated from a human fibroblast cDNA library by colony hybridization. The total length of the cloned cDNA was 518 base pairs with an open reading frame of 333 base pairs. The 111-amino acid sequence deduced from the nucleotide sequence of the cDNA is 85% homologous to that of bovine QP-C and contains only a single additional amino-terminal methionine. This implies that the human QP-C is synthesized without a presequence which is required for import of most nuclear-encoded mitochondrial proteins into mitochondria.     

Intergenus cell fusion between L-form cells of Pseudomonas aeruginosa and Escherichia coli

Intergenus cell fusion of prokaryotic bacteria was demonstrated for the first time; namely, fusion products doubly resistant to streptomycin and tetracycline were produced by polyethylene glycol treatment of a mixture of the streptomycin-resistant L-form of Pseudomonas aeruginosa and tetracycline-resistant L-form of Escherichia coli.     

Effects of Some Growth Regulators and Benzoic Acid Derivatives on Flower Initiation and Root Elongation of Pharbitis nil, Strain Kidachi

Seedlings of Pharbitis nil, strain Kidachi, were grown undercontinuous light at 20°C in vessels containing 5,000-mlnutrient solution, 24 plants per vessel. NAA (0.005–0.5µM), GA₃ (0.1–0.5 µM), kinetin (0.5–5µM), benzyladenine (0.05–5 µM) or abscisicacid (4 µM) added to the nutrient solution induced long-dayflowering, and the flowering was always accompanied by suppressionof root elongation. 3,4-Dichlorobenzoic acid (0.05–10µM) and some other benzoic acid derivatives which arehighly effective for the induction of flowering in Lemna paucicostataalso showed similar effects. Neither NAA, kinetin nor 3,4-dichlorobenzoicacid applied via the apical part of the hypocotyl could causeflowering or suppression of root elongation. Thus, the flower-inducingeffect of the above substances was presumed to be secondaryto the suppression of root elongation. Ethrel (1–50 µM)added to the nutrient solution suppressed root elongation, butdid not induce flowering probably because it has flower-inhibitingactivity. ¹ This paper is dedicated to the memory of Dr. Joji Ashida,the first president of the Japanese Society of Plant Physiologists. (Received December 15, 1982; Accepted February 25, 1983)