Determination of the spatial structure of insectotoxin 15A from Buthus erpeus by (1)H-NMR spectroscopy data]

The solution structure of insectotoxin 15A (35 residues) from scorpion Buthus eupeus was determined on the basis of 386 interproton distance restraints 12 hydrogen-bonding restraints and 113 dihedral angle restraints derived from 1H NMR experiments. A group of 20 structures was calculated with the distance geometry program DIANA followed by the restrained energy minimization with the program CHARMM. The atomic RMS distribution about the mean coordinate position is 0.64 +/- 0.11 A for the backbone atoms and 1.35 +/- 0.20 A for all atoms. The structure contains an alpha-helix (residues 10-20) and a three-stranded antiparallel beta-sheet (residues 2-5, 24-28 and 29-33). A pairing of the eight cysteine residues of insectotoxin 15A was established basing on NMR data. Three disulfide bridges (residues 2-19, 16-31 and 20-33) connect the alpha-helix with the beta-sheet, and the fourth one (5-26) joins beta-strands together. The spatial fold of secondary structure elements (the alpha-helix and the beta-sheet) of the insectotoxin 15A is very similar to those of the other short and long scorpion toxins in spite of a low (about 20%) sequence homology.     

The root-knot nematode resistance gene (Mi) in tomato: construction of a molecular linkage map and identification of dominant cDNA markers in resistant genotypes

A dominant allele at the Mi locus on chromosome 6 of tomato (Lycopersicon esculentum Mill) confers resistance to three species of root-knot nematodes (Meloidogyne). The resistance, which is associated with a localized necrotic response, was originally introduced into tomato from the wild species Lycopersicon peruvianum. As a step towards the molecular cloning of Mi, we have identified closely linked DNA markers from both cDNA and genomic DNA libraries as restriction fragment length polymorphisms (RFLPs). DNA from tomato populations segregating for nematode resistance was analyzed to generate a high-resolution genetic map of this region. Additional information on gene order was obtained by comparing the size of the introgressed L. peruvianum chromosomal segment within a collection of nematode-resistant tomato lines. Among the four cDNA markers that are tightly linked to Mi, three are dominant, i.e. L. peruvianum-specific. One cDNA marker corresponds to a gene family comprising 20-30 members, one of which is diagnostic for all nematode-resistant genotypes tested. The presence of non-homologous sequences around the Mi gene may contribute to the suppression of recombination in this region of the genome in crosses heterozygous for Mi. The potential of 'walking' from closely linked markers to Mi is discussed.     

白暨豚正常心电图的初步探讨

1980年以来,我们测定了白鱀豚(Lipotes vexillifer)“淇淇”和“珍珍”的心电图,并与人和其他海豚的心电图作了比较,从而确定了白鱀豚心电图常规导联的联接方法,并比较完整地描述了白鱀豚正常心电图的特征。研究发现,白鱀豚的心电图各波、段和间期的正常范围基本与人的相近,但T波的特征与人不同,人的T波与同导联的主波方向一致,而白鱀豚的T波却正好相反。P—R间期明显比人的延长。本研究将为白鱀豚心血管疾病的诊断提供重要依据。     

森林土壤氮转化的微生物功能研究

本文研究了不同林型下土壤(A+6层和A_1层)微生物、土壤酶活性在森林土壤氮转化中的作用。结果表明不同林型下土壤具有不同的固氮作用、反硝化作用、氨化作用和硝化作用速率,即阔叶林>针阔混交林>针叶林。已经证明,固氮作用主要存在于森林土壤的A_1层,反硝化作用主要存在于A_0层。森林土壤存在2种硝化作用过程,即由自养微生物所引起的自养硝化作用过程和异养微生物所引起的异养硝化作用过程。它的存在与林型有关,某些森林土壤中这2种硝化作用过程都存在,如针阔混交林下的A_0层和A_1层。有些林型下土壤,则以异养硝化作用过程为主,如针叶林的A_0层。     

中国大鲵视网膜的光镜和扫描电镜研究

用光镜和扫描电镜观察了大鲵视网膜各类细胞的形态及分布, 对视细胞和节细胞进行计数。视网腊中三个核层及两个网状层分布均匀,无中央凹。每张视网膜的视细胞总数约130000,节细胞约8000,视杆与视锥之比为8.5：1。扫描电镜下,视杆外节表面的小叶间沟清晰;视杆视锥外节均有从内节伸出的20-30条萼状突起;核周体表面亦有20-30条细胞质突起。文中还报道了幼体视细胞的形态及密度。讨论了上述结构的机能。     

The TIS11 primary response gene is a member of a gene family that encodes proteins with a highly conserved sequence containing an unusual Cys-His repeat.

The TIS11 primary response gene is rapidly and transiently induced by both 12-O-tetradecanoylphorbol-13-acetate and growth factors. The predicted TIS11 protein contains a 6-amino-acid repeat, YKTELC. We cloned two additional cDNAs, TIS11b and TIS11d, that contain the YKTELC sequence. TIS11, TIS11b, and TIS11d proteins share a 67-amino-acid region of sequence similarity that includes the YKTELC repeat and two cysteine-histidine containing repeats. TIS11 gene family members are not coordinately expressed: (i) unlike TIS11, the TIS11b and TIS11d mRNAs are detectable in quiescent Swiss 3T3 cells and are not dramatically induced by 12-O-tetradecanoylphorbol-13-acetate; (ii) cycloheximide superinduction does not occur for TIS11b and TIS11d; and (iii) unlike TIS11, TIS11b expression is extinguished in PC12 pheochromocytoma cells.     

Enzyme activities in Chrysosporium strains

390 strains of Chrysosporium were screened for their ability to produce enzymes. All strains produced: catalase, phosphatase, lipase, amylase, DNAse and phosphoamidase. No strains showed: valine arylamidase, oxidase, -galactosidase, urease, pectolase, protease nor RNAse.     

Structure and expression of the human XPBC/ERCC-3 gene involved in DNA repair disorders xeroderma pigmentosum and Cockayne's syndrome

The human XPBC/ERCC-3 was cloned by virtue of its ability to correct the excision repair defect of UV-sensitive rodent mutants of complementation group 3. The gene appeared to be in addition implicated in the human, cancer prone repair disorder xeroderma pigmentosum group B, which is also associated with Cockayne's syndrome. Here we present the genomic architecture of the gene and its expression. The XPBC/ERCC-3 gene consists of at least 14 exons spread over approximately 45 kb. Notably, the donor splice site of the third exon contains a GC instead of the canonical GT dinucleotide. The promoter region, first exon and intron comprise a CpG island with several putative GC boxes. The promoter was confined to a region of 260 bp upstream of the presumed cap site and acts bidirectionally. Like the promoter of another excision repair gene, ERCC-1, it lacks classical promoter elements such as CAAT and TATA boxes, but it shares with ERCC-1 a hitherto unknown 12 nucleotide sequence element, preceding a polypyrimidine track. Despite the presence of (AU)-rich elements in the 3'-untranslated region, which are thought to be associated with short mRNA half-life actinomycin-D experiments indicate that the mRNA is very stable (t 1/2 greater than 3h). Southern blot analysis revealed the presence of XPBC/ERCC-3 cross-hybridizing fragments elsewhere in the genome, which may belong to a related gene.     

Distribution of salmon gonadotrophin releasing-hormone in the brain and pituitary of the sea bass (Dicentrarchus labrax)

Summary The distribution of salmon gonadotrophin-releasing hormone (sGnRH) was studied in the brain and pituitary of two-year-old immature sea bass (Dicentrarchus labrax) by means of an enzymoimmunoassay (EIA) for sGnRH and immunocytochemistry. The EIA for sGnRH is a competitive assay using a tracer made of sGnRH coupled to acetylcholinesterase from an electric eel. The separation of free and bound tracer is achieved by coating the plates with mouse anti-rabbit IgG monoclonal antibodies. Displacement curves generated by sGnRH and extracts from pituitary and different brain regions showed a good parallelism allowing the assay to be used for sGnRH measurements in this species. Although all parts of the brain contained measurable levels of sGnRH, the highest concentrations were found in the pituitary, the olfactory bulbs and the telencephalon. These data were confirmed by immunocytochemistry. Cell bodies were found in the olfactory bulbs, ventral telencephalon, preoptic region and mediobasal hypothalamus. Immunoreactive fibers could be observed in all parts of the brain including the optic tectum, the cerebellum (corpus and valvula), the vagal lobe, the medulla oblongata and the rostral spinal cord. In most cases, these fibers do not form well defined bundles; however, there was clearly a continuum of immunoreactive fibers, extending from the olfactory bulbs to the pituitary, and along which all the cell bodies described above were located. In the ventral telencephalon and the preoptic region, clear pictures of varicose positive fibers contacting immunoreactive perikarya could be observed. These data indicate that sGnRH is most likely an endogenous peptide in the brain of the sea bass, although the presence of other forms of GnRH cannot be excluded at this point. This study also demonstrates that the general organization of the GnRH systems in the sea bass is highly similar to what has been described in most freshwater teleost species, and provides basis for further studies on the neuroendocrine control of gonadotrophin release in this commercially important species.     

Variation of geosmin content in Anabaena cells and its relation to nitrogen utilization

The addition of the proper amount of ammonium to the culture medium containing nitrate as nitrogen source enhanced the growth rate of Anabaena viguieri. The amount of geosmin produced by these cells varied with the concentrations of ammonium added. A negative correlation between the amount of geosmin produced and of the growth rate of cells was revealed. This was also found in cells grown on various forms of nitrogen sources. Without supply of any nitrogen compound, this organism is capable of fixing gaseous nitrogen, and under these conditions the cells grew relatively slowly. However, they produced more geosmin (per unit protein mass) than cells grown in the presence of combined nitrogen. The isolation of heterocysts, in which nitrogen was fixed, showed that these cells produced higher amounts of geosmin than vegetative cells. The possible relation of nitrogen assimilation to the production of geosmin in the cells was discussed.