博莱霉素-Ce(Ⅲ)对DNA的切断机理初探

根据外切核酸酶Ⅲ酶解博莱霉素-Ce(Ⅲ)［BLMA5-Ce(Ⅲ)］作用过的双链直线型DNA时, 酶解速率明显增大, 酶解产物除5′-dAMP、5′-dGMP、5′-dCMP和5′-dTMP 4种单核苷酸外, 还有其他成分存在的实验事实, 推测出BLMA5-Ce(Ⅲ)在DNA双链的特定部位沿5′→3′的方向切断磷酸二酯键, 使DNA的双链上形成多个暴露的3′-OH末端.     

银额果蝇自然群体分化过程中的细胞遗传学

对我国大陆银额果蝇的分布及其细胞遗传学进行了广泛的调查,发现了一种值得注意的新核型。该核型结构兼有早已认可的长、短两大类基本核型的特征,即核型中的两条同源４号染色体为１长１短型。含新核型的群体分布于我国大陆东南沿海一带的上海、福州、厦门和深圳。而且,这些自然群体内还出现“１长１短型”、“长型”和“短型”重叠并存的多态现象。跟踪研究表明,新核型具有不稳定的遗传性,能世代传递,它的频率随世代增长而降低,并不是突然消失。但是,在上海、福州群体内出现的“长型”至第十五代之后却全部消失。这种新核型大概是银额果蝇自然演化过程中的中间过渡核型,是该果蝇种群分化中的细胞遗传学变异的过渡表征     

Extended models of the ventilatory response to sustained isocapnic hypoxia in humans

Liang, Pei-Ji, Daphne A. Bascom, and Peter A. Robbins.Extended models of the ventilatory response to sustained isocapnic hypoxia in humans. J. Appl. Physiol. 82(2): 667-677, 1997.The purpose of this study was to examine extensions of a modelof hypoxic ventilatory decline (HVD) in humans. In the original model (model I) devised by R. Painter, S. Khamnei, and P. Robbins(J. Appl. Physiol. 74: 2007-2015, 1993), HVD is modeledentirely by a modulation of peripheral chemoreflex sensitivity. In thefirst extension (model II), a more complicated dynamic is usedfor the change in peripheral chemoreflex sensitivity. In the secondextension (model III), HVD is modeled as a combination ofboth the mechanism of Painter et al. and a component that isindependent of peripheral chemoreflex sensitivity. In all cases, aparallel noise structure was incorporated to describe the stochasticproperties of the ventilatory behavior to remove the correlation of theresiduals. Data came from six subjects from a study by D. A. Bascom, J. J. Pandit, I. D. Clement, and P. A. Robbins (Respir. Physiol.88: 299-312, 1992). For model II, there was a significantimprovement in fit for two out of six subjects. The reasons for thiswere not entirely clear. For model III, the fit was againsignificantly improved in two subjects, but in this case the subjectswere those who had the most marked undershoot and recovery ofventilation at the relief of hypoxia. In these two subjects, thechemoreflex-independent component contributed ~50% to total HVD.In the other four subjects, the chemoreflex-independent componentcontributed ~10% to total HVD. It is concluded that in somesubjects, but not in others, there may be a component of HVD thatis independent of peripheral chemoreflex sensitivity.

     

Non-crystallographic symmetry of crystal of neutral phospholipase A2 from Agkistrodon halys Pallas

Agkistrodotoxin, a neutral phospholipase A₂ with high presynaptic neurotoxicity from the venom of Agkistrodon halys Pallas, has been crystallized by hanging drop vapor diffusion method. The crystal belongs to P2₁ space group with the cell dimensions a = 10.836 nm, b=8.486nm, c = 7.082nm, β=109.87$ showing C2 pseu-do-symmetry. Diffraction data to 0. 26 nm resolution have been collected on a Siemens X-200B area detector. C2 pseu-do-symmetry suggests that there exists a non-crystallographic two-fold axis parallel to crystallographic b axis. Self-rotation function calculation with different integrated radius and resolution ranges using the program POLARRFN yields four stable high peaks corresponding to three more non-crystallographic two-fold axis and one special non-crystal-lographic symmetry. The molecules in the asymmetric unit are suggested to be arranged in a manner of "dimer of dimers" by inference.     

A ketoreductase gene from Streptomyces mycarofaciens 1748 DNA involved in biosynthesis of a spore pigment

An efficient plasmid transformation system forS. mycarofaciens 1748 has been established. In order to determine the function of MKR gene in S.mycarofaciens 1748, the gene disruption experiment was carried out. For this purpose the plasmid pKC1139 was used. A recombinant strain with white spore appeared, in contrast to the grey-colour spore of S.myarofaciens 1748. This suggested that homologous recombination between plasmidborne MKR gene sequence and the chromosome of S.mycarofaciens 1748 had occurred. A Southern hybridization experiment using a-³²P-labelled MKR gene as probe indicated that the desired integration event had occurred in the recombinant. The result of gene disruption showed that the alteration of this gene in the chromosome of S.mycarofaciens 1748 made sporulating colonies remain white instead of taking on the typical grey colour of sporulating wild type colonies, suggesting that MKR gene is involved in the biosynthesis of a spore pigment. The recombinant strain was incubated with fermentation medium optimised for midecamycin production. A TLC assay showed that the recombinant strain produced midecamycin in quantities comparable to that ofS. mycarofaciens 1748. A pCN8B12 was a clone from genomic library of midecamycin producing strain which contained a 28-kb DNA insert. The 28-kb DNA fragment contained act I-homologous and act III-homologous regions. he PKS (act I-homologous) and MKR (act III-homologous) genes that define spore pigment of midecamycin producing strain were Jocalized by restriction endonuclease digestion with pCN8B12, indicating that they are separated by about 10 kb DNA. The polyketide synthase gene cluster of simila; organization has not been reported yet. Project supported by the National Natural Science Foundation of China.     

Sublocalization of an Ataxia-Telangiectasia Gene Distal to D11S384 by Ancestral Haplotyping In Costa Rican Families

In an effort to localize a gene for ataxia-telangiectasia (A-T), we have genotyped 27 affected Costa Rican families, with 13 markers, in the chromosome 11q22-23 region. Significant linkage disequilibrium was detected for 9/13 markers between D11S1816 and D11S1391. Recombination events observed in these pedigrees places A-T between D11S1819 and D11S1960. One ancestral haplotype is common to 24/54 affected chromosomes and roughly two-thirds of the families. Inferred (ancestral) recombination events involving this common haplotype in earlier generations suggest that A-T is distal to D11S384 and proximal to D11S1960. Several other common haplotypes were identified, consistent with multiple mutations in a single gene. When considered together with all other evidence, this study further sublocalizes the major A-T locus to ≈200 kb, between markers S384 and S535.     

横断山地区果蝇三新种(双翅目：果蝇科)

横断山地区果蝇三新种（双翅目：果蝇科）张文霞,梁醒财（北京大学生命科学学院北京１００８７１）（中国科学院昆明动物研究所昆明６５０２２３）’果蝇属果蝇亚属Ｄｒｏｓｏｐｈｉｌａ（Ｄｒｏｓｏｐｈｉｌａ）的ｍｅｌａｎｄｅｒｉ种组由Ｗｈｅｅｌｅｒ１９４９年建立...     

The use of 2-hydroperoxytetrahydrofuran as a reagent to sequence cytosine and to probe non-Watson-Crick DNA structures.

2-Hydroperoxytetrahydrofuran (THF-OOH) can be employed to sequence cytosine (C) and to probe for non-canonical DNA structures involving C. Using 32P-labeled oligomers and a DNA restriction fragment, it is demonstrated that THF-OOH has a strong preference for Cs in single-stranded (s-s) DNA regions, and in bulges, loops and mismatches. The reactivity of C is diminished below pH 6.0, but is not affected by substitution of 5-methylcytosine. To demonstrate the utility of the reagent, it is directly compared to methoxylamine and chloroacetaldehyde, two other reagents commonly used to chemically probe C residues in non-Watson-Crick DNA structures.     

中国蝙蝠体翼手恙螨属一新种（蜱螨亚纲：恙螨科）

本文记述采自江西的翼手恙螨属一新种,由毛翼手恙螨,新种Ｃｈｉｒｏｐｔｅｌｌａ ｃｕｒｖｉｓｅｔｏｓａ ｓｐ．ｎｏｖ．,模型标本保存于江西医学院寄生虫学教研室。