BACILLUS THURINGIENSIS PROTOXIN STRUCTURE AND SYNTHESIS

报道了苏云金芽孢杆菌(Bt.)德尔塔- 由基因序列推导出的内毒素具有某些保守区域 这很可能反映了类似的行动模式。包裹体 含有三角洲内毒素(或原毒素)的昆虫可溶解 幼虫肠道并转化为与特定细胞膜结合的毒素 感受器。毒素然后插入膜中形成或改变 阳离子毛孔。测序的毒素对不同来源的幼虫具有活性 昆虫目包括鳞翅目、鞘翅目和双翅目。在这些人中 目标昆虫是那些危害树木和庄稼以及媒介的昆虫。 用来对付病原体。事实上，世卫组织正在雇用B.T.与世隔绝在非洲 病媒控制。 因为可能会有一种共同的行动模式，一种 原毒素基因已被选择进行广泛的诱变分析，以 评估原毒素分子的不同部分的贡献 到炮制、特异性和毒性。既有站点定向的，也有 突变寡核苷酸技术将用于改变特定的 基因的残基或区域。突变的基因将被克隆回来 进入B.T.。从而可以将纯包裹体分离出来用于生物分析和 体外囊泡结合和转运实验。一种对 各保守区对这些进程的贡献应该是 有助于新毒素的设计，有助于阐明毒素的作用模式 行动和理解抵抗的基础。 大多数B.T.分离株含有多个原毒素基因，这些基因 表达的程度不同。总的来说，原毒素基因是庞大的。 差异表达的质粒会受到基因复制的影响 数量、质粒稳定性和转录因子的可用性。 这些特殊的参数将在至少两个分离株中进行检测 用基因特异性探针检测原毒素基因含量，稳定 状态mRNA水平和特定基因的存在或不存在 原毒素编码质粒。了解原毒素的调节 合成对于评价新的药物的疗效是很重要的。 用于通过交配和/或转化构建新菌株的菌株 用于确定特定基因在特定环境中的稳定性 隔离。

The amino acid sequences of all Bacillus thuringiensis (B.t.) delta- endotoxins deduced from gene sequences share certain conserved regions which very likely reflect a similar mode of action. Inclusions containing the delta-endotoxins (or protoxins) are solubilized in insect larval guts and converted to toxins which bind to specific cell membrane receptors. The toxins then insert into the membrane to form or alter cation pores. The sequenced toxins are active on larvae from different insect orders including Lepidoptera, Coleoptera and Diptera. Among the target insects are those which damage trees and crops as well as vectors for pathogens. In fact, WHO is employing a B.t. isolate in Africa for vector control. Since there is likely to be a common mode of action, one protoxin gene has been selected for extensive mutagenic analysis in order to assess the contribution of various portions of the protoxin molecule to processing, specificity and toxicity. Both site-directed and mutagenic oligonucleotide techniques will be used to alter specific residues or regions of the gene. The mutated genes will be cloned back into B.t. so that pure inclusions may be isolated for bioassays and for in vitro vesicle binding and transport experiments. An understanding of the contribution of various conserved regions to these processes should be helpful in the design of new toxins, for elucidating the mode of action and for understanding the basis for resistance. Most B.t. isolates contain multiple protoxin genes which are expressed to different extents. In general, protoxin genes are on large plasmids so differential expression could be influenced by gene copy number, plasmid stability and the availability of transcription factors. These particular parameters will be examined in at least two isolates employing gene-specific probes to measure protoxin gene content., steady state mRNA levels and the presence or absence of a particular protoxin-encoding plasmid. Understanding the regulation of protoxin synthesis would be important for the evaluation of the efficacy of new isolates, for constructing new strains by mating and/or transformation and for determining the stability of certain genes in a particular isolate.