2.5 Virus rescue.
The eight gene segments of GX/18 and GD/104 were inserted into the
vRNA–mRNA bidirectional transcription vector pBD to rescue rGX/18,
rGD/104 and the reassortant and mutant viruses as described
previously(Ping et al., 2008). Mutations
were introduced into HA gene in the background of GX/18 and GD/104 by
site-directed mutagenesis (Invitrogen) according to the manufacturer’s
protocol. Gene-specific primers used in study were shown in Table 1, and
all the rescued viruses were completely sequenced to avoid the unwanted
mutations.