人铜锌超氧化物歧化酶基因在乳酸乳球菌中的食品级表达

以lacF基因为食品级选择标记，构建了乳酸乳球菌食品级基因表达系统，并进而实现了人铜锌超氧化物歧化酶基因在乳酸乳球菌中的食品级表达。首先构建了含有lacF基因两侧同源DNA序列(0.5kb)的整合型质粒pUCEmDE，通过pUCEmDE与乳酸乳球菌MG5267染色体上单拷贝的乳糖操纵子之间的同源双交换，构建了lacF基因缺失突变的食品级受体菌WZ103 (Lac-)，并经PCR及Lac表型检测所验证。然后构建了互补质粒pMG36eF，其lacF基因的表达受组成型的强启动子P32的控制。将其电转化导入WZ103后，Lac+表型得到恢复，表明WZ103中lacF基因的功能可被互补质粒pMG36eF上的lacF基因互补。随后，以互补质粒pMG36eF为基础，构建了不含任何抗生素抗性选择标记的人铜锌超氧化物歧化酶基因的食品级表达质粒pWZ104。通过非变性聚丙烯酰胺凝胶电泳和SOD活性凝胶染色分析，检测到WZ103(pWZ104)中Cu/Zn SOD的表达，并且具有生物活性。

Food-grade Expression of Human Cu/Zn-superoxide Dismutase Gene in Lactococcus lactis

A food-grade gene expression system in L. lactis using the lacF gene as selection marker was constructed and further used for food-grade expression of human Cu/Zn superoxide dismutase (Cu/Zn SOD). Firstly, an integrative plasmid pUCEmDE containing homologous fragments with 0.5kb flank sequences of the lacF gene was constructed. The lacF gene was in-frame deleted by double cross-over between the plasmid pUCEmDE and the chromosomal DNA in L.lactis MG5267 and resulted in a food-grade host WZ103 that was confirmed by PCR and Lac phenotype examination. After that, a complementary plasmid pMG36eF in which the lacF gene was controlled by the strong constitutive promoter P 32 was electroporated into WZ103 and resulted in the restoration of Lac + phenotype, indicating that the lacF function in WZ103 could be complemented by the lacF gene in pMG36eF. Finally, a food-grade plasmid pWZ104 used for the expression of Cu/Zn SOD was constructed, in which the lacF gene was used as a selective marker instead of any antibiotic resistance genes. Expressed Cu/Zn SOD in WZ103(pWZ104) was demonstrated and showed biological activity through non-denatured PAGE and SOD activity gel-staining.