TABLE 1.

Silent mutations in the coding sequences of PA, PB1, and PB2 segments

VirusWild-type sequenceProtein sequenceMutant sequenceaRelative packaging efficiency (%)bVirus titer in 293T supernatant (no. of PFU/ml)c
Wild type>752 × 106
PA-m15sGCATTGAGA671ALR673GCTCTCCGT25 × 105
PB1-m12sGAGCTCAGACGG752ELRR755GAATTGCGTAGA0.43 × 104
PB2-m6sTCTAGC741SS742AGCTCG0.42.4 × 105
  • a Changed nucleotides are underlined.

  • b Relative packaging efficiency was determined as described in Materials and Methods.

  • c Wild-type and mutant viruses were reconstituted in 293T cells by using the 17-plasmid system, and the infectious particles in the supernatants collected at 48 h posttransfection were quantified by a plaque assay.