Abstract:To obtain lactase preparations with high activity，a lactase gene from Aspergillus oryzae was synthesized based on the preference of Kluyveromyces lactis GG799 codon.The synthesized lactase gene from Aspergillus oryzae was cloned into the expression vector pKLAC1，resulting in pKLAC1-lacA.The pKLAC1-lacA was linearized by SacⅡand transformed into K.lactis GG799 by electrotransformation.Positive clones were screened by yeast carbon base（YCB）plates containing 5 mmol/L acetamide.A multi-copy recombinant strain lacA-1 was obtained by whole-cell polymerase chain reaction（PCR）verification.The recombinant strain secreted extracellularlactase with biologicalactivity by sodium dodecylsulfate polyacrylamide gelelectrophoresis（SDS-PAGE）and thin-layer chromatography（TLC）analysis.The lactase activity of the culture supernatant was 120.65 U/mL after 120 hours shaking flask cultivation.This research successfully expressed recombinant lactase gene from A.oryzae in K.lactis GG799 and the expressed protein showed high activity，which provided the basis for the study on the large-scale production of recombinant lactase gene using K.lactis GG799 expression system.