| 1. | Effect of avec gene deletion on avermectins production in streptomyces avermitilis
基因缺失对产素调控的影响 |
| 2. | An extensive program of chemical modificaton can also be carried out to discover more active avermectins
这种有白点的菌落形态与灰色菌落类似，可能为放线菌中形成的异核体。 |
| 3. | The total amount of avermectins b were only about 0 . 5 ~ 2 % of those produced by the parental strain olm73 - 12 . this study suggests that t
在281个突变株中，还筛选到了2个突变株，其发酵产物几乎全部为有效组分阿维菌素b1 ， b2组分仅占5 。 |
| 4. | According to the cloned gene cluster , people can use genetical technology to obtain the genetical strains which can produce more potent and non - toxical avermectins and its derivatives
这使得人们可利用基因工程技术来构建工程菌，增加有效组分的产出和生产新型的阿维菌素。 |
| 5. | The avermetins are a group of closely related macrocylic lactones with exceedingly high activity against helminths and anthropods . this paper review the biosyntheticpathway of the avermectins and the organization of the biosynthetic gene cluster which many groups have analysed and cloned
阿维菌素为一种典型的次级代谢产物，生物合成途径复杂，现在基本上对每一步合成途径的基因及其所编码的酶都有所了解。 |
| 6. | Shaking flask experiments and hplc analyses showed that 99 isolates still produced four components of avermectins b , in which the yields of avermectins b in 82 isolates were only about 0 . 1 ~ 2 % of those produced by the parental strain olm73 - 12 . 2 of 82 isolates were confirmed to be the correct gene replacement mutants by pcr and sequence analysis . the mutant only producing avermectins bl was not detected
摇瓶发酵和hplc分析结果表明，有99个突变株仍然产阿维菌素b的4个组分，其中82株的发酵单位很低，仅为出发菌株olm73 - 12的0 . 1 2 ，从中挑取2株经pcr扩增和测序验证，均发生了正确的基因取代；没有检测到仅产b1的突变株，这表明阿维菌素b2组分的产生并不是因为阿维菌素pks上dh2的部分活性所造成。 |
| 7. | In addition to avermectins , s . avermitilis produces oligomycin , a strongly toxic compound . gene deletion vector pxl05 was used to disrupt oligomycin polyketide synthase ( pks ) encoding genes ( olma ) in streptomyces avermitilis cz8 - 73 , the producer of anthelmintic avermectins b and the cell growth inhibitor oligomycin . olma gene cluster in the chromosome was displaced by deletion allele on the plasmid via double crossover
本研究以产阿维菌素b和寡霉素的阿维链霉菌cz8 - 73为出发菌株，构建了基因缺失载体pxl05 ，并将其转入cz8 - 73中，通过缺失载体和染色体之间的同源双交换，对染色体上长达90kb的寡霉素聚酮合酶( pks )基因簇( olma )进行了缺失。 |
| 8. | In this study , the avermectin - producing strain streptomyces avermitilis was studied and the avermectin biosynthesis gene cluster in the genomic dna of streptomyces avermitilis s - 2 was altered by the method of gene engineering . insertion inactivation of aved gene in the cluster by introducing apramycin resistance gene into aved gene resulted in the disappearance of " a " components of avermectins . when avec gene was inactivated by the same way , four " 1 " components were lost and only " 2 " components , the potential precursor of ivermectin , were accumulated
将该基因簇中的aved基因通过插入外源的安普霉素抗性基因片段使其失活，导致发酵产物中4个a组分(不需要的组分)的消失；将基因簇中的avec基因通过同样手段，使其失活，导致发酵产物中4个“ 1 ”组分的消失，而主要积累“ 2 ”组分(进一步改造可成为伊维菌素的前体b _ 2组分) 。 |
| 9. | Content : avermectins are a class of drugs which have been found wide usage against a board spectrum of nematodes and arthropods , many of which are important endoparasites and ectoparasites of animals . avermectin bi is a common agriculture pesticide produced by the actinomycete streptomyces avermitilis and registered for worldwide use
正文：阿维菌素类药物( avermectins ， avms )属大环内酯类抗生素，由于其优异的驱虫活性和较高的安全性，被视为目前最为优良、应用最广泛的兽用驱虫药。 |
| 10. | Ivermectins ( a mixture containing more than 80 % of 22 , 23 - dihydroavermectin bla and less than 20 % of 22 , 23 - dihydroavermectin b1b ) , which have the same effective antiparasitic activities and the lower level of toxic side - effects than avermectins , are currently synthesized by chemically reducing the double bond between c22 and c23 of avermectins b1
阿维菌素b1在c - 22 , 23位的化学加氢还原产物称为伊维菌素( ivermectins ) ，具有与阿维菌素相同的杀虫活性，但毒性更低，更安全。目前国内外报道的伊维菌素生产均是用化学还原法，生产成本很高。 |
