Briefly, 50–100 ng of the purified influenza PCR amplicon was mixed with 50 ng of the linearinfluenza vector pJY2013, 2 l of ExnaseTMII and 4 l of 5× CE IIbuffer. The mixture was incubated at 37◦C for 30 min followed by5 min on ice, and then transformed into regular chemically competent cells for recombinants. The primers used in this study arelisted in