3.1 Strains, plasmids, reagents and substrates
Escherichia coli strains DH5α were used for propagation and manipulation of plasmids, and P. pastoris SMD1168 was used for protein expression. The plasmids pPIC9K were used for gene cloning and expression, respectively. The tool enzymes of Sal I, T4 DNA ligase, Taq DNA polymerase, DNA marker, and d NTP were obtained from Takara Biomedical Technology (Beijing) Co., Ltd. And the antibiotic ampicillin was obtained from Solarbio/Life Sciences (China) Co., Ltd. (Beijing, China). All primers were synthesized by Invitrogen/Life Technologies (Carlsbad, USA). The substrate 4-nitrophenyl-α-L-rhamnopyranoside (p NPR), was purchased from Sigma Co. Ltd. (St. Louis, MO, USA). All other reagents used in this study were of analytical grade.