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根据已知大肠杆菌志贺氏菌样毒素Ⅱ型变异体Ｂ亚单位（ＳＬＴ－ⅡｖＢ）基因序列，设计并合成 ３条２对引物，以大肠杆菌 Ｏ_１３８基因组为模板，通过聚合酶链式反应（ＰＣＲ）分别扩增出 ２０４ ｂｐ的基因序列及包含一段信号肽的 ２６１ ｂｐ基因序列。将这两段 ＤＮＡ分别克隆进表达性载体质粒ＰＹＡ３３３４的ＥｃｏＲⅠ和ＢａｍＨⅠ位点之间，经地高辛标记探针进行Ｓｏｕｔｈｅｒｎ杂交和酶切分析鉴定，并对两条扩增片段进行序列测定。结果表明，扩增产物的大小与设计相符，扩增与克隆的片段为ＳＬＴ－ⅡｖＢ基因的特异性片段。
According to the known gene sequence of Escherichia coli Shigella toxin Ⅱ variant B subunit (SLT-ⅡvB), three pairs of primers were designed and synthesized. The Escherichia coli O_138 genome was used as a template to detect PCR) were amplified 204 bp gene sequence and a signal peptide 261 bp gene sequence. The two DNA fragments were cloned into the EcoRI and BamH I sites of the expression vector plasmid PYA3334 respectively. Southern blotting and digestion analysis were carried out by digoxigenin-labeled probe. The two amplified fragments were sequenced. The results showed that the size of the amplified product was consistent with the design. The amplified and cloned fragments were specific fragments of SLT-ⅡvB gene.