Abstract:[Objective] We analyzed the evolution and mutations of PB1 genes among seasonal H3N2 influenza viruses, to reveal the molecular characteristics and evolutionary trend of PB1 genes. [Methods] We analyzed PB1 and PB1-F2 genes by molecular biological software with 82 A/H3N2 viruses from 1968 to 2014 in China, 81 viruses isolated from Jiangsu Province between 2012 and 2014, 6 swine influenza viruses and 4 avian influenza viruses. [Results] PB1 segments in China showed high nucleic acid and amino acid sequence similarity (90.91% to 100%, 96.91% to 100%). The phylogenetic tree of PB1 genes was divided into 4 clusters. Strains isolated from 2002 to 2014 located in Clade IV and 1968 to 1994 were in Clade II and III. SIVs dispersed in Clade I, II, IV suggesting a reassortment of PB1genes may occurred in swine population between A/H3N2 and other subtypes. Compared to strains isolated from 1968 to 1994, the amino acid substitution of PB1 gene (52, 113, 179, 216, 576, 586, 619, 621 and 709) was observed between 2002 and 2014 with adaptive changes. Truncated PB1-F2 protein included 52, 34, 25, 24 and 11 aa (SIV). The mutation of the key virulence sites did not appear among Human A/H3N2 influenza. [Conclusion] PB1 segments of A/H3N2 influenza virus underwent stable evolution and mutation, the truncated PB1-F2 protein has become a new trend in its evolutionary process. This finding suggests that we should pay great attention on the reassortment of PB1 genes and its mutation on key virulence sites. This emphasizes the importance of virus surveillance of A/H3N2 virus.
