Fig. 1.
Phylodynamics of global influenza B virus. Relative genetic diversities and temporal phylogenies of the HA and NA gene segments of the Victoria (A and B) and Yamagata lineages (C and D). Among the Victoria lineages, gray tip circles represent viruses in absence of HA deletions. Orange tip circles denote clade 1A.1 viruses with 2-aa deletions at positions 162–163 of the HA protein. Green, pink, and blue tip circles denote different clades (1A.2–1A.4) harboring a 3-aa deletion at positions 162–164 of the HA protein. For each gene phylogeny, trunk amino acid substitutions are mapped at the backbone of each tree. Amino acid substitutions in bold indicate potential N-linked glycosylation sites. (E) Three-dimensional structure of the trimeric HA (PDB ID code: 4FQM) and (F) tetrameric NA (PDB ID code: 3K36) proteins of B/Brisbane/60/2008 (Victoria lineage) and B/Perth/211/2001(Yamagata lineage) as reference, respectively. Trunk amino acid substitutions that occurred in the Victoria clade 1A.1–1A.3 and the Yamagata clade 3A viruses are mapped.