Escherichia coli JM107 was preserved in our laboratory. pQE-30Xa vector was purchased from Qiagen (Germany). pET-28a vector was purchased from Novagen (Germany). pMD-19T(simple)and pLVX-ZsGreen1-N1 vectors were purchased from Takara (Japan). Anti-His antibody (HRP conjugated) was purchased from Abmart (China). DNA sequencing and the primers used in this study were synthesized at the Beijing Genomics Institute (China)