目的 为研究大肠埃希菌中色氨酸合成酶α亚基编码基因(trpA)的表达，利用λ-Red系统将trpA、黄色荧光蛋白基因(yfp)、氯霉素抗性编码基因(cat)融合片段敲入基因组中。方法 将trpA、yfp、cat基因进行融合PCR，获得重组片段，转化入MG1655菌株中，利用pKD46编码的λ-Red系统将片段重组入基因组中，经PCR验证及测序鉴定正确后，荧光显微镜观察融合蛋白表达。结果 成功获得trpA-yfp-cat重组片段，转化入MG1655菌株中获得阳性克隆，经测序鉴定正确。荧光显微镜观察可见细菌胞质内弥散分布黄色荧光，表明trpAyfp融合表达片段成功地在MG1655菌株中表达。结论 运用λ-Red系统可将trpA-yfp融合片段敲入MG1655菌株基因组中原位替换trpA基因，通过观察YFP蛋白的表达间接反映trpA基因的表达，具有不改变trpA基因自身功能和细菌生长的优点，为进一步研究大肠埃希菌色氨酸合成途径奠定基础。

Objective To investigate the expression of tryptophan synthase α subunit-encoding gene (trpA) of Escherichia coli (E. coli), fusion fragment of trpA, yellow fluorescent protein gene (yfp) and chloramphenicol-encoding gene (cat) was knocked into E.coli strain MG1655 genome using λ-Red system. Methods Target genes trpA, yfp and cat were amplified by PCR, and the recombinant fragment was obtained by fusion PCR. The recombinant fragment was transformed into E.coli strain MG1655 harboring genes of λ-Red system in plasmid pKD46. After PCR checking and sequencing confirmation, the fusion protein expression was observed by fluorescence microscopy. Results The recombinant fragment trpA-yfp-cat was successfully obtained and transformed into MG1655, and the positive clones were screened out and confirmed by sequencing. The yellow fluorescence was observed throughout the bacterial cytoplasm, indicating that trpA-yfp fusion protein was successfully expressed in MG1655. Conclusion The trpA gene could be replaced by trpA-yfp fusion fragment in situ using λ-Red system, and its expression could be reflected indirectly by observing the expression of yellow fluorescent protein. The function of trpA and bacterial growth have not been changed, which lays foundation for the further study of E.coli tryptophan synthesis.