3.1. Selection of RT–PCR primers
To obtain a sufficient amount of viral RNA and to facilitate
successful amplification of all gene segments, the viruses
were passaged for at least for two generations until an obvious
cytopathic effect appeared (data not shown). To synthesize
cDNA from all genes of the influenza A virus, the first twelve
nucleotide sequence was chosen based on the 3-termini of all
segments of the virus. The BLAST system was used to compare
the sequence of synthesized cDNA with that of the expected
sequence in GenBank, which showed that the 3-termini of all
segments was highly conserved among all vRNA segments with
the exception that the fourth base may be “A” or “G” in the
cDNA of different influenza viruses. Therefore, to improve the
complementarity of this primer, the fourth base of this primer
was designed by using “R” instead of “A”. To distinguish this
primer from that of described previously, this primer was named
Uni12(M).