NYMC X-197 derived the HA and NA gene segments from the wt virus and the M and NS gene segments from A/PR/8/1934. A. HA: lane 1: A/PR/8/1934 undigested; 2 and 3: A/PR/8/1934 digested with PvuII and HindIII, respectively; 4: A/Brisbane/11/2010 undigested; 5 and 6: A/Brisbane/11/2010 digested with PvuII and HindIII, respectively; 7: NYMC X-197 undigested; 8 and 9: NYMC X-197 digested with PvuII and HindIII, respectively. B. NA: lane 1: A/PR/8/1934 undigested; 2 and 3: A/PR/8/1934, digested with BsgI and Eco57I, respectively; 4: A/Brisbane/11/2010 undigested; 5 and 6: A/Brisbane/11/2010 digested with BsgI and Eco57I, respectively; 7: NYMC X-197 undigested; 8 and 9: NYMC X-197 digested with BsgI and Eco57I, respectively. C. M: lane 1: A/PR/8/1934 undigested; 2: A/PR/8/1934 digested with BsgI; 3: A/Brisbane/11/2010 undigested; 4: A/Brisbane/11/2010 digested with BsgI; 5: NYMC X-197 undigested; 6: NYMC X-197 digested with BsgI. D. NS: lane 1: A/PR/8/1934 undigested; 2 and 3: A/PR/8/1934 digested with SmlI and XmnI, respectively; 4: A/Brisbane/11/2010 undigested; 5 and 6: A/Brisbane/11/2010 digested with SmlI and XmnI, respectively; 7: NYMC X-197 undigested; 8 and 9: NYMC X-197 digested with SmlI and XmnI, respectively.