Molecular cloning and sequencing of infC, the gene encoding translation initiation factor IF3, from four enterobacterial species

Abstract Translation initiation factor IF3 plays a crucial role in initiation of protein synthesis in bacteria. In order to elucidate the IF3 structural elements required for these functions, the evolutionary conservation of IF3 and its gene, infC , was investigated. Homologous infC sequences from Salmonella typhimurium, Klebsiella pneumoniae, Serratia marcescens and Proteus vulgaris were amplified by the polymerase chain reaction and sequenced. Analysis of these sequences, as well as that from Bacillus stearothermophilus , revealed several regions (e.g. residues 62–73 and 173–177) of absolute sequence conservation, suggesting an important role for these regions in IF3 function.     

Algae in mosquito breeding sites and the effectiveness of the mosquito larvicide Bacillus thuringiensis H-14

The presence of cyanobacteria generally decreased the effectiveness of Bacillus thuringiensis H-14 (BTI) as a mosquito larvicide. The effect was more pronounced when the mosquito larvae were exposed to BTI in the presence of several cyanobacterial strains. No synergistic or antagonistic effect between the -endotoxin from BTI and the hepatotoxin from cyanobacteria was seen. Neurotoxic cyanobacterial strains caused very fast paralysis in mosquito larvae; the decreases in the effectiveness of BTI when tested in combination with a neurotoxic strain might be due to the effect of this paralytic action on the feeding rate of the mosquito larvae.     

HPLC separation of the enantiomers of nicotine and nicotine-like compounds

A sensitive and reproducible HPLC method utilizing a commercially available chiral α₁-acid glycoprotein (AGP) phase has been developed to separate and quantify the enantiomers of nicotine. The method is suitable for routine use as indicated by column life. The quantification of (R/S:0.05/99.95)-nicotine or (R/S:99/1)-nicotine was possible. In addition, the separation or at least partial separation of the enantiomers of nornicotine and nornicotine-derived compounds was achieved. © 1993 Wiley-Liss, Inc.     

Acid-Catalyzed nucleophilic substitution and racemization of 3-methoxy-N-desmethyldiazepam enantiomers in methanol

pK_a1 values of 3-methoxy-N-desmethyldiazepam in acetonitrile and methanol containing various acid concentrations were determined by spectrophotometry to be 3.5 and 1.3, respectively. Temperature-dependent racemization of enantiomeric 3-methoxy-N-desmethyldiazepam in methanol containing 0.5 M H₂SO₄ was studied by circular dichroism spectropolorimetry and the racemization reactions were found to follow apparent first-order kinetics. Thermodynamic parameters of the racemization reaction were found to be: E_act = 18.8 kcal/mol, and at 25°C: ΔH^? = 18.3 kcal/mol, ΔS^? = ?14.8 entropy unit, and ΔG^? = 22.7 kcal/mol, respectively. The racemization had an isotope effect (k_H/k_D) of 1.6 at 42°C. Based on the results of this report and those of earlier reports by other investigators, a nucleophilically solvated C3 carbocation intermediate resulting from either a P (plus) or an M (minus) conformation is proposed to be an intermediate and responsible for the stereoselective nucleophilic substitution and the subsequent racemization of 3-methoxy-N-desmethyldiazepam enantiomers. © 1993 Wiley-Liss, Inc.     

Influence of phosphate ion on the fluorescence of 3-fluorotyrosine

Summary 3-Fluorotyrosine fluorescence is quenched effectively by phosphate ions not only by a dynamic but also by a static mechanism owing to H-bond complex formation in ground state. 3-Fluorotyrosine pK_a values both in the ground and first excited state (8.3 and 4, respectively) are appreciably lower than those of tyrosine, thus promoting 3-fluorotyrosinate ion formation in the excited state. Additional emission owing to 3-fluorotyrosinate ion (near 350 nm) may be taken erroneously for tryptophan fluorescence.     

Phototropism in hypocotyls of radish. VI. No exchange of endogenous indole-3-acetic acid between peripheral and central cell layers during first and second positive phototropic curvatures

Using a physicochemical method, the distribution of endogenous indole-3-acetic acid (IAA) was measured in the peripheral and central cell layers, as well as in the illuminated and shaded sides of phototropically stimulated radish hypocotyls (Raphanus sativus var. hortensis f. gigantissimus Makino). The IAA was evenly distributed over the illuminated and shaded sides in the first and second positive phototropic curvatures induced by a pulse or a continuous unilateral illumination with blue light. Also, no net exchange of the IAA between the peripheral and central cell layers was observed during these curvatures. These results suggest that phototropism of radish hypocotyls cannot be described by the Cholodny-Went theory.     

Repetitive Micronuclear Divisions in the Absence of the Macronucleus During Conjugation of Paramecium caudatum

ABSTRACT. The germinal micronucleus divides six times during conjugation of Paramecium caudatum : this includes two meiotic divisions and one mitosis of haploid nuclei during mating, and three mitoses of a fertilization nucleus (synkaryon). Microsurgical removal of the macronucleus showed that micronuclei were able to divide repeatedly in the absence of the macronucleus, after metaphase of meiosis I of the micronucleus and also after synkaryon formation. When the macronucleus was removed after the first division of synkaryon, in an extreme case the synkaryon divided five times and produced 32 nuclei, compared to three divisions and eight nuclei produced in the presence of the macronucleus. Treatment with actinomycin D (100 μ /ml) inhibited the morphological changes of the macronucleus during conjugation and induced a multimicronucleate state in exconjugants. However, in other cells, it induced production of a few giant micronuclei. We conclude that the micronucleus is able to undergo repeated divisions at any stage of conjugation in the absence of the macronucleus once the factor(s) for induction of the micronuclear division has been produced by the macronucleus. The macronucleus may also produce a regulatory factor required to stop micronucler division.     

The zygote and proembryo of alfalfa: quantitative,three-dimensional analysis and implications for biparental plastid inheritance

Summary Genetic studies have demonstrated biparental inheritance of plastids in alfalfa. The ratio of paternal to maternal plastids in the progeny varies according to the genotypes of the parents, which can be classified as strong or weak transmitters of plastids. Previous cytological investigations of generative cells and male gametes have provided no consistent explanation for plastid inheritance patterns among genotypes. However, plastids in the mature egg cells of a strong female genotype (6–4) were found to be more numerous and larger than in mature eggs of a weak female genotype (CUF-B), and the plastids in 6–4 eggs are positioned equally around the nucleus. In CUF-B, the majority of plastids are positioned below (toward the micropyle) the mid level of the nucleus, which is the future division plane of the zygote. Since only the apical portion of the zygote produces the embryo proper, plastids in the basal portion were predicted to become included in the suspensor cells and not be inherited. In the present study, we examined zygotes and a two-celled proembryo from a cross between CUF-B and a strong male genotype (301), a cross that results in over 90% of the progeny possessing paternal plastids only. Our results indicate that the distribution of plastids observed in the CUF-B egg cell is maintained through the first division of the zygote. Further, paternal plastids are similarly distributed; however, within the apical portion of the zygote and in the apical cell of the two-celled proembryo, the number of paternal plastids is typically much greater than the number of maternal plastids. These findings suggest that maternal and paternal plastid distribution within the zygote is a significant factor determining the inheritance of maternal and paternal plastids in alfalfa.