Natural history and functional divergence of protein tyrosine kinases

Cellular signaling is important for many biological processes including growth, differentiation, adhesion, motility and apoptosis. The protein tyrosine kinase (PTK) supergene family is the key mediator in cellular signaling in metazoans, directly associated with a variety of human diseases. All PTKs contain a highly conserved catalytic kinase domain, in spite of variable multi-domain structures. Within each PTK gene family, members exhibit functional divergence in substrate-specificity or temporal/tissue-specific expression, although their primary function is conserved. After conducting phylogenetic analysis on major PTK gene families, we found that the expanding of each PTK family was likely caused by gene or genome duplication event(s) that occurred before the emergence of teleosts but after the vertebrate-amphioxus split. We further investigated the evolutionary pattern of functional divergence after gene duplication in those gene families. Our results show that site-specific shifted evolutionary rate (altered functional constraint) is a common pattern in PTK gene family evolution.     

Morphologies and phylogenetic classification of cellulolytic myxobacteria

The evolutionary distances of the 16S rDNA sequences in cellulolytic myxobacteria are less than 3%, which units all the strains into a single genus, Sorangium. The size of myxospores and the shape of sporangioles, rather than fruiting body colors or swarm morphologies are consistent with the changes of the 16S rDNA sequences. It is suggested that there are at least two species in the genus Sorangium: one includes strains with small myxospores and spherical sporangioles, and the color of the fruiting bodies is normally orange or brown, though sometimes yellow or black. The second species has large myxospores, polyhedral sporangioles with many inter-cystic substrates, and normally deep brown to black color.     

Selenium and sulfur accumulation and soil selenium dissipation in planting of four herbaceous plant species in soil contaminated with drainage sediment rich in both selenium and sulfur

Four selenium (Se) nonaccumulator plant species, including a forage grass species, Tall Fescue (Festuca arundinacea Schreb.), a forage legume species, Alfalfa (Medicago sativa L.), a wetland species, Rush (Juncus tenuis Wild.), and a dry-land alkaline soil species, Saltgrass (Distichlis spicata L.), were grown in soil contaminated by agricultural drainage sediment having elevated levels of Se and sulfur (S). The above-ground plant tissues were consecutively harvested five times and examined for Se and S accumulation. Plant tissue Se concentrations ranged from 23.0 mg kg-1 to 8.3 mg kg-1. Tissue S concentrations ranged from 3239 mg kg-1 to 7034 mg kg-1. Both tissue Se and S concentrations were significantly different between harvests, species, and species/harvest interactions. Total Se accumulation by the plant biomass harvested ranged from 0.3 to 1.3 mg per soil column and total S accumulations ranged from 87.5 to 321.1 mg per soil column. The reduction in the percentage of total soil Se after 24 weeks growth of the plant species ranged from 12.0% in the Tall Fescue planting to 17.3% in the Rush planting. Over 90% of the soil Se losses were unidentified losses and leaching of Se was prevented. The accumulations of Se and S in the plant biomass were very small compared with the total soil Se and S losses, but substantial amounts of total soil Se (12.0 to 15.0%) and S (28.0 to 50.9%) inventories were dissipated by the growing and harvesting of the plants. The soil S concentration was several hundred times higher than the soil Se concentration, but Se accumulation by the plants and Se dissipation from the soil were not impaired by the high level of soil sulfur. For natural grassland habitat restoration, such as at the Kesterson Wildlife Refuge in the Central Valley of California, or for restoration of large-scale Se contaminated agricultural lands, Se nonaccumulator plant species are favorable candidates, because the possibility of introducing Se toxicity into the food chain can be minimized.     

上下视野空间选择性注意的ERP研究

该文主要研究上、下视野空间选择性注意早期所诱发的ＥＲＰ反应,探讨注意上、下视野视觉信息处理的特征与差别。１０名被试的主要实验果为：１）对上、下视野的选择注意产生类似于注意左、右视野时Ｐ１、Ｎ１,Ｐ２的相对增强;２）偶极子定位显示,上、下视野刺激的早期注意反应（Ｐ１）以交叉方式投射到枕区,即下视野刺激的注意反应偏向枕区的背侧,而上视野刺激的注意反应偏向枕区的腹侧;３）上下视野的早期注意反应（Ｐ１）具     

Evolutionary Patterns of Gene Families Generated in the Early Stage of Vertebrates

In this paper we have analyzed 49 vertebrate gene families that were generated in the early stage of vertebrates and/or shortly before the origin of vertebrates, each of which consists of three or four member genes. We have dated the first (T₁) and second (T₂) gene duplications of 26 gene families with 3 member genes. The means of T₁ (594 mya) and T₂ (488 mya) are largely consistent to a well-cited version of two-round (2R) genome duplication theory. Moreover, in most cases, the time interval between two successive gene duplications is large enough that the fate of duplicate genes generated by the first gene duplication was likely to be determined before the second one took place. However, the phylogenetic pattern of 23 gene families with 4 members is complicated; only 5 of them are predicted by 2R model, but 11 families require an additional gene (or genome) duplication. For the rest (7 families), at least one gene duplication event had occurred before the divergence between vertebrate and Drosophila, indicating a possible misleading of the 4:1 rule (member gene ratio between vertebrates and invertebrates). Our results show that Ohno's 2R conjecture is valid as a working hypothesis for providing a most parsimonious explanation. Although for some gene families, additional gene duplication is needed, the credibility of the third genome duplication (3R) remains to be investigated. Received: 13 December 1999 / Accepted: 7 April 2000     

Novel Pathway for Conversion of Chlorohydroxyquinol to Maleylacetate in Burkholderia cepacia AC1100

Burkholderia cepacia AC1100 metabolizes 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) via formation of 5-chlorohydroxyquinol (5-CHQ), hydroxyquinol (HQ), maleylacetate, and β-oxoadipate. The step(s) leading to the dechlorination of 5-CHQ to HQ has remained unidentified. We demonstrate that a dechlorinating enzyme, TftG, catalyzes the conversion of 5-CHQ to hydroxybenzoquinone, which is then reduced to HQ by a hydroxybenzoquinone reductase (HBQ reductase). HQ is subsequently converted to maleylacetate by hydroxyquinol 1,2-dioxygenase (HQDO). All three enzymes were purified. We demonstrate specific product formation by colorimetric assay and mass spectrometry when 5-CHQ is treated successively with the three enzymes: TftG, TftG plus HBQ reductase, and TftG plus HBQ reductase plus HQDO. This study delineates the complete enzymatic pathway for the degradation of 5-CHQ to maleylacetate.     

富勒烯的生物活性研究进展

90年代初以来,富勒烯类化合物的生物活性逐渐引起人们的注意,初步研究表明在抗艾滋病毒、酶活性抑制、切割DNA、光动力学治疗等方面具有独特的功效.此类化合物在生化、医学、药物学等领域有良好的应用前景.     

微生物法生产普鲁兰酶的研究

对产普鲁兰酶的出发菌株进行筛选和诱变,使酶活从22．10u／ml提高到了40．77u／ml,酶活提高了84．4％。随后对菌体产酶培养基进行了确定和优化,得到最佳发酵培养基,在此培养基下,菌体产酶达46．76u／ml,为原酶活的114．7％。     

维甲酸对鼻咽癌细胞生长、表型和瘤基因表达的作用

研究了维甲酸（ＲＡ）对鼻咽癌细胞生长、表型和癌基因表达的作用．用ＲＡ诱导鼻咽癌细胞,绘制诱导前后的细胞曲线,观察细胞形态,并用Ｎｏｒｔｈｅｒｎ杂交和ＤＮａｓｅⅠ超敏感区分析法检测基因表达和调控．结果表明,ＲＡ能显著抑制鼻咽癌细胞的生长,前５ｄ下降约５０％．ＲＡ处理后的细胞从典型的多边形形态变成扁平、细长,类似纤维细胞状的形态．ＲＡ诱导前ｃ－ｍｙｃ基因和ｃ－Ｈａ－ｒａｓ基因ＨＮＥ２细胞中高表达,而诱导后ｃ－ｍｙｃ基因表达水平急剧下降,ｃ－Ｈａ－ｒａｓ基因无明显改变．在实验中还发现ＲＡ诱导前后的ｃ－ｍｙｃ基因和ｃ－Ｈａ－ｒａｓ基因中一些重要的超敏感位点和它们的功能．由实验结果可得到如下结论：ＲＡ能促进鼻咽癌细胞分化,通过对染色体上调控位点的作用来抑制ｃ－ｍｙｃ基因的表达,ＤＮａｓｅⅠ超敏感位点与细胞的分化程度、细胞的组织特异性和基因表达状态有关,ｃ－ｍｙｃ基因可通过不同的调控方式而失活．