Primer pJY2013 F Primer pJY2013 F contains15 nts which is the reverse complement of the 15 conserved nts of the reverse primer for each influenza fragment, and primer pJY2013 R contains 15 nts which is the reverse complement of the15 conserved nts of the forward primer for each influenza fragment.Therefore, the linear influenza rescuing vector contains 15 identi-cal nts with the PCR amplicon for each influenza fragment at both 5 and 3 terminus. For in vitro recombination, the influenza PCRamplicon was recombined with the linear universal vector generated by PCR according to the description in Section 2. Then, there combinants were transformed into E. coli competent cells for selection of positive clones..