极端耐热木聚糖酶基因在枯草芽孢杆菌中的整合表达

目的:为了在枯草芽孢杆菌中整合表达极端耐热木聚糖酶。方法:将嗜热网球菌(Dictyoglomus thermophilum)Rt46B.1的极端耐热木聚糖酶基因xynB通过穿梭载体pDL整合到B.subtilis168染色体上,使其实现表达。结果:极端耐热木聚糖基因在枯草芽孢杆菌中成功整合并表达。结论:基因工程菌B.subtilis168-xynB能外泌表达极端耐热木聚糖酶,且表达水平为0.732IU/mL,比在大肠杆菌中的高。酶学性质表明,此酶分子量约为24kD,其最适反应温度为85℃,最适反应pH值为6.5,且在弱碱性条件下稳定。     

Crossover Position Drives Chromosome Remodeling for Accurate Meiotic Chromosome Segregation

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DNA elimination and its relation to quantities in the macronucleus of Tetrahymena

The macronucleus of Tetrahymena contains a large number of DNA molecules of subchromosomal size. They belong to about 270 species each one occurring at an average number of 45 copies Macronuclei divide unequally and nothing is known of segregation control. This and the elimination and degradation of DNA during macronuclear amitosis make the clonal stability of macronuclei a problem of qualitative and quantitative control on a subchromosomal level. We studied the contribution of DNA elimination to the quantitative composition of the macronucleus cytophotometrically in single cells of different strains. This was done under standard conditions and under conditions known to influence the amount of macronuclear DNA. The following results were found: Elimination of DNA occurs at almost every division. The size of the elimination body is highly variable but still positively correlated with the macronuclear DNA content. In T. thermophila the amount of eliminated DNA is 2.5% of the G2 content and is not dependent on the growth state. It varies with species, amounting to as much as 8% in T pigmentosa. During conditions which increase the macronuclear DNA content, very little DNA is eliminate. On the other hand, large amounts are eliminated under other conditions causing the macronuclear DNA content to decrease. DNA to be eliminated at division is synthesized at the same time as bulk DNA. We developed a computer program which helps us study the effects of DNA elimination and unequal divisions upon the copy numbers of subchromosomal DNA classes. The result indicates that in a given cell line at least one of the DNA molecules becoms extinct after 60 generations which we expect would cause the cell's extinction and restrict a clone's life to 60 generations. As this does not happen in nature, there must be some control of the copy numbers preventing their extinction during vegetative multiplication. Whether elimination increases or decreases the imbalance of genes remains to be investigated. © 1992 Wiley-Liss, Inc.     

Role of intercellular contacts in generating an asymmetric mitotic apparatus in the Tubifex embryo

The 2-cell stage embryo of Tubifex is composed of a smaller cell, AB, and a larger cell, CD. At the second cleavage, the CD-cell divides unequally. The mitotic apparatus (MA) involved in this division is organized asymmetrically: the MA pole to be segregated to a smaller cell is flattened and truncated, and associated with the anterior cortex facing the AB-cell, while the other pole is symmetric and located more centrally. The present study was undertaken to elucidate the mechanism that generates asymmetry in the MA organization in CD-cells. When CD-cell nuclei, which are normally located near the anterior cortex, were displaced toward the posterior end of the cell (i.e. opposite AB-cells) by centrifugation, MA assembled ectopically there, and were bilaterally symmetric in organization. Similar symmetric MA were formed in isolated CD-cells, which divided more equally than intact cells. This equality of cell division was dramatically reduced if the anterior surface of isolated CD-cells formed contact with other cells, such as AB-, C- and 4D-cells. The MA that formed in these reconstituted embryos were asymmetric in organization; one MA pole was always found to be truncated and apposed to the cortical site at the cell contact. Symmetric MA were also observed in cytochalasin-treated embryos. Together with the finding that one of the MA poles is physically attached to the anterior cortex of the intact CD-cell, these results suggest that factors generating asymmetry in the spatial organization of MA poles reside at the anterior cortex of the CD-cell and that this cortical mechanism is dependent upon cell contacts.     

On the possible occurrence of anisospory in some Hepaticae

PANT, D. D. & SINGH, R., 1989. On the possible occurrence of anisospory in some Hepaticae. Possible anisospory is reported for the first time in four species of Hepaticae, viz., Targionia indica Udar, Targionia hypophylla L., Cyathodium aureo-nitens Griff. (Mitt.), Cyathodium barodae Chavan. The report is based on observations of wide variations in size of spores comparable with those of anisosporous mosses of the family Orthotrichacae.     

Characterization of swine leukocyte antigen alleles and haplotypes on a novel miniature pig line,Microminipig

Microminipigs are extremely small‐sized, novel miniature pigs that were recently developed for medical research. The inbred Microminipigs with defined swine leukocyte antigen (SLA) haplotypes are expected to be useful for allo‐ and xenotransplantation studies and also for association analyses between SLA haplotypes and immunological traits. To establish SLA‐defined Microminipig lines, we characterized the polymorphic SLA alleles for three class I (SLA‐1, SLA‐2 and SLA‐3) and two class II (SLA‐DRB1 and SLA‐DQB1) genes of 14 parental Microminipigs using a high‐resolution nucleotide sequence‐based typing method. Eleven class I and II haplotypes, including three recombinant haplotypes, were found in the offspring of the parental Microminipigs. Two class I and class II haplotypes, Hp‐31.0 (SLA‐1*1502–SLA‐3*070102–SLA‐2*1601) and Hp‐0.37 (SLA‐DRB1*0701–SLA‐DQB1*0502), are novel and have not so far been reported in other pig breeds. Crossover regions were defined by the analysis of 22 microsatellite markers within the SLA class III region of three recombinant haplotypes. The SLA allele and haplotype information of Microminipigs in this study will be useful to establish SLA homozygous lines including three recombinants for transplantation and immunological studies.     

基因重复研究进展

基因复制是基因通过不等交换,反转录转座或由全基因组复制等途径产生一个与原基因相似的基因或碱基序列,它与生物体基因组大小的进化、新基因的起源、物种的分化以及基因抗突变的能力大小等都密切相关。本文综述了复制基因的产生和保留机制、选择作用、分化的途径以及复制基因进化速率等方面的相关研究,揭示了基因复制对于生物进化的重要性,以引起大家对该领域的了解与关注。关键词：基因复制;复制基因;不等交换;反转录转座;全基因组复制     

Synthesis and characterization of Fe(III)(3-CH3O-qsal)2PF6 · nH2O (n = 0, 2)

Compounds Fe^III(3-CH₃O-qsal)₂PF₆ · nH₂O (n = 0, 2) (1, 1 · 2H₂O) were synthesized and characterized: the structure of 1 and the magnetic properties of both compounds were determined. Compound 1 · 2H₂O presents properties characteristic of high-spin Fe(III), while 1 presents properties of low-spin Fe(III) with an onset of a gradual spin crossover at ca. 300 K.