The 498 bp conventional PCR target amplicon band on agarose gel was cut and the DNA was recovered and purified by TIANquick DNA Purification system (Tiangen Corp., Beijing, China) according to the instruction manual of the product. The product was ligated into pGM-T vector (Tiangen Corp., Beijing, China) and transformed into E.coli DH5α competent cells. Recombinant plasmid (designated as pAHV-1) was extracted using TIANprep plasmid extraction kit (Tiangen Corp., Beijing, China). Presence of the target DNA insert was confirmed by PCR amplification and sequencing.