Widner W R, Whiteley H R
Department of Microbiology, University of Washington, Seattle 98195.
J Bacteriol. 1990 Jun;172(6):2826-32. doi: 10.1128/jb.172.6.2826-2832.1990.
Two highly related crystal protein genes from Bacillus thuringiensis subsp. kurstaki HD-1, designated cryIIA and cryIIB (previously named cryB1 and cryB2, respectively), were used to study host range specificity. Their respective gene products are 87% identical but exhibit different toxicity spectra; CryIIA is toxic to both mosquito and tobacco hornworm larvae, whereas CryIIB is toxic only to the latter. Hybrids of the cryIIA and cryIIB genes were generated, and their resultant gene products were assayed for toxicity. A short segment of CryIIA corresponding to residues 307 through 382 was shown to be sufficient for altering host range specificity-i.e., when this region replaced the corresponding segment of CryIIB, the resulting hybrid protein acquired toxicity against mosquitoes. The CryIIA and CryIIB polypeptides differ by only 18 amino acids in this region, indicating that very few amino acid changes can have a substantial effect on the toxicity spectra of these proteins.
来自苏云金芽孢杆菌库尔斯塔克亚种HD-1的两个高度相关的晶体蛋白基因，分别命名为cryIIA和cryIIB（之前分别命名为cryB1和cryB2），被用于研究宿主范围特异性。它们各自的基因产物有87%的同一性，但表现出不同的毒性谱；CryIIA对蚊子和烟草天蛾幼虫都有毒性，而CryIIB仅对后者有毒性。构建了cryIIA和cryIIB基因的杂交体，并对其产生的基因产物进行了毒性测定。已证明CryIIA对应于307至382位残基的一小段足以改变宿主范围特异性——也就是说，当该区域取代CryIIB的相应片段时，产生的杂交蛋白获得了对蚊子的毒性。CryIIA和CryIIB多肽在该区域仅相差18个氨基酸，这表明极少的氨基酸变化就能对这些蛋白质的毒性谱产生实质性影响。
