Transition from somatic to meiotic pairing and progressional changes of the synaptonemal complex in spermatocytes of Aedes aegypti

Aedes aegypti spermatocytes were reconstructed from electron micrographs. The species has tight somatic pairing of the chromosomes, and there are therefore no classical leptotene and zygotene stages, but rather a gradual transition from somatic pairing to meiotic pairing (= pachytene). The term prepachytene has been used for the transitory stage. The first visible sign of impending meiosis was a reorganization of the chromatin, which resulted in the formation of spaces (synaptic spaces) in the chromatin, about the width of the synaptonemal complexes (SCs). Diffuse material, possibly precursor material for the SC, was present in the spaces. Later short pieces of complex were formed throughout the nucleus. Late prepachytene, pachytene, and diplotene complexes were reconstructed. Each chromosome occupied a separate region of the nucleus. The complexes became progressively shorter from prepachytene (maximum complement length 289 m) to diplotene (175 m). The thickness of the SCs increased from prepachytene to pachytene and probably decreased again during diplotene. At the beginning of diplotene the lateral elements (LEs) separated, and the single LEs became two to three times thicker than the LEs of the SC. The centromeres were at all stages attached to the nuclear membrane, whereas the telomeres were free in the nucleoplasm during pachytene and diplotene. A heterochromatic marker was present on chromosome 1 near the sex determining locus, and a diffuse marker on chromosome 3 near the nucleolus organizer region. After breakdown of the complexes, polycomplexes were present in the nucleus.     

Scorpion toxins from Centruroides noxius and Tityus serrulatus. Primary structures and sequence comparison by metric analysis.

The complete primary structures of toxin II-14 from the Mexican scorpion Centruroides noxius Hoffmann and toxin gamma from the Brazilian scorpion Tityus serrulatus Lutz and Mello have been determined. Cleavage of toxin gamma after Met-6 with CNBr produced the 55-residue peptide 7-61, which maintained the four disulphide bonds but was not toxic to mice at a dose 3 times the lethal dose of native toxin gamma. Pairwise comparison by metric analysis of segment 1-50 of toxin gamma and the corresponding segments from two other South American scorpion toxins, five North American scorpion toxins, nine North African scorpion toxins and one Central Asian scorpion toxin showed that the three Brazilian toxins are intermediate between the North American and North African toxins. This result is consistent with the hypothesis that the South American and African continents were joined by a land connection in the distant past.     

Subunit composition of photosystem I and identification of center X as a [4Fe-4S] iron-sulfur cluster

A photosystem I (PS-I) preparation from barley (Hordeum vulgare L.) containing the reaction center protein P700-chlorophyll a-protein 1 (CP1) and smaller polypeptides with apparent molecular masses of 18, 16, 14, 9.5, 9, 4, and 1.5 kDa has been analyzed with respect to subunit stoichiometry. CP1 contains two homologous subunits with approximate masses of 82 kDa. CP1 and the smaller polypeptides were isolated, and the amino acid composition of each component and of the PS-I preparation was determined. Based on the amino acid composition data and the determined ability of each isolated polypeptide to bind Coomassie Brilliant Blue, the PS-I complex is shown to contain 1 mol of each of the homologous 82-kDa polypeptides as well as 1 mol of the 18-, 16-, 9.5-, and 9-kDa polypeptides for each mol of P700. The total polypeptide mass of the PS-I complex is 209 kDa excluding tryptophan and approximately 220 kDa including tryptophan. The two 82-kDa subunits present/P700 provide cysteine residues for binding only one Fe-S center. In conjunction with the earlier reported binding of four iron and four acid-labile sulfides to CP1/P700 (H?j, P. B., Svendsen, I., Scheller, H. V., and M?ller, B. L. (1987) J. Biol. Chem. 262, 12676-12684), this demonstrates the center X is a [4Fe-4S] cluster and eliminates the possibility of center X being composed of two [2Fe-2S] clusters.     

The effective diffusion coefficient and the distribution constant for small molecules in calcium-alginate gel beads

The effective diffusion coefficient, D(e), and the distribution constant, K(i), for selected mono- and disaccharides and organic acids were determined in homogeneous calcium-alginate gel with and without entrapped bacteria. Results were obtained from transient concentration changes in well-stirred solutions of limited volume, in which the gel beads were suspended. The effective diffusioncoefficients and the distribution constants were estimated by fitting mathematical model predictions to the experimental data using a nonlinear model fitting program (MODFIT). Both single solute diffusion and multiple solute diffusion were performed. A small positive effect was obtained onthe values of D(e) for the system of multiple solute diffusion; however, the values of K(i) were not significantly influenced. For the nine solutes tested, D(e) for 2% Ca-alginate gel beads was found to be approximately 85% of the diffusivity measured in water. The effects on D(e) and K(i), for lactose and lactic acid were determined for variations of alginate concentration, pH, temperature, and biomass content in the beads. D(e) decreased linearly for both lactose and lactic acid with increasing cell concentration in the Ca-alginate gel. K(i), was constant for both lactose and lactic acid with increasing cell concentration. D(e) was significantly lower at pH 4.5 than at pH 5.5 and 6.5 for both lactose and lactic acid. Furthermore, D(e) seemed to decrease with increased alginate concentration in the range of 1% to 4%. The diffusion rate increased with increasing temperature, and the activation energy for the diffusion process for both lactose and lactic acid was constant in the temperature range tested. (c) 1995 John Wiley & Sons Inc.     

Separation of macromolecules in isotachophoresis systems involving single or multiple counterions

The isotachcophoresis principle provides unique opportunities for rational designs of fractionation procedures involving charged molecules. Theoretically any two charged molecules that are soluble under the experimental conditions involved can be physically separated if their electrophoretic net mobilities differ only slightly in the electrophoresis medium used. A theoretical and practical outline is presented that enables the reader to set up this fractionation system and on a rational basis develop fractionation procedures for a given set of charged macromolecules by isotachophoresis with simple and well characterized ampholytes as spacer substances. The planning of preparative experiments in this approach is based on results obtained from rapid analytical screens on a microgram scale. The report includes an appendix containing the theoretical basis for computation of buffer compositions in the isotachophoretic steady state with mono/polyvalent constituents in systems involving one or more counterions and controlled amounts of interferiong ions.     

Studies on Tyzzer's disease in rats.

An outbreak of an epidemic disease occurred in a specified-pathogen-free (SPF) breeding colony of rats. The clinical signs and the post-mortem findings were characteristic for Tyzzer's disease. The causative agent, Bacillus piliformis, was demonstrated microscopically in ileum, liver and myocardium, and transmitted to mice where its pathogenicity appeared to be similar to that of another strain isolated from mice. B. piliformis from spontaneously-infected rats was demonstrated by indirect immunofluorescence technique. By means of the same technique it was found that the fluorescence antibody titre obtained of the individual sera from spontaneously-infected mice, rats and rabbits was the same, whether the antigen employed was organisms isolated from rats or mice. By testing sera from healthy rats in 3 different colonies by use of immunofluorescence technique, antibodies were found in several sera.     

The primary structure of Escherichia coli K12 2-deoxyribose 5-phosphate aldolase. Nucleotide sequence of the deoC gene and the amino acid sequence of the enzyme

The sequence of the deoC gene of Escherichia coli K12 and the amino acid sequence of the corresponding protein, deoxyriboaldolase, has been established. The protein consists of 259 amino acids with a molecular weight of 27 737. The purified enzyme may exist both as a monomer and as a dimer. On the basis of amino acid composition, molecular weight and catalytic properties, the enzymes from E. coli and Salmonella typhimurium seem to be almost similar. They belong to the class I aldolases, which form Schiff base intermediates. Using data for the S. typhimurium enzyme, the lysine residue involved in the active site in the E. coli enzyme was tentatively identified.     

A plant serpin gene. Structure, organization and expression of the gene encoding barley protein Z4

A 3133-bp nucleotide sequence of the gene Paz1 on chromosome 4 of barley, encoding endosperm protein Z4, has been determined. The sequence includes 1079 bp 5' upstream and 523 bp 3' downstream of the coding region. The 1079-bp 5' upstream region of the gene shows little similarity to 5' regions of other sequences genes expressed in the developing cereal endosperm. The coding sequence is interrupted by one 334-bp-long intron (bases 1497-1830). The deduced amino acid sequence, which was corroborated by peptide sequences, consists of 399 amino acids and has a molecular mass of 43,128 Da. This sequence confirms protein Z4 to be a member of the serpin superfamily of proteins. The similarity with other members of the family expressed as amino acids in identical positions is in the order of 25-30% and pronounced in the carboxy-terminal half of the molecule. Sequence residues assumed to form clusters stabilizing the tertiary structure are highly conserved. Protein Z4 is synthesized in the developing endosperm without a signal peptide and protein Z4 mRNA was evenly distributed among the free and membrane-bound polyribosomes of the endosperm cell. An internal hydrophobic region of 21 amino acids (residues 36-56) may serve as a signal for targeting the polypeptide into the lumen of the endoplasmic reticulum. The gene for protein Z4 could not be detected in the barley variety Maskin and some of its descendants. The 'high-lysine' allees, lys1 (Hiproly barley) and lys3a (Bomi mutant 1508) on chromosome 7, enhance and repress, respectively, the expression of the protein Z4 gene. Also, 1554 bp of another 8-kbp fragment of the barley genome Paz psi, similar to the protein-Z4-coding region, have been determined. Small insertions and deletions and the presence of an internal stop codon identify this fragment as part of a pseudogene related to the protein Z4 gene.