title: Molecular characterization of the HA gene of influenza type B viruses.
abstract: Nucleotide sequences of the HA1 subunit of influenza B viruses isolated in Portugal between 1994 and 2003 influenza winter seasons were analyzed by the Neighbor-Joining algorithm and rates of HA1 evolution estimated by linear regression. From 1994 to 2002, all influenza B viruses studied were of the Yamagata lineage. Strains isolated from 1994 to 1996, 1996 to 1999, and 1999 to 2002 revealed a high similarity with B/Beijing/184/93, B/Yamanashi/166/98, and B/Sichuan/379/99, respectively, and strains isolated during 1994-1995, 1996-1997, and 1998-1999 clustered in more than one branch of the phylogenetic tree. Victoria-related strains reappeared during 2002/2003 and formed only one branch in the phylogenetic tree revealing a closer relationship to B/Shandong/7/97. Evolutionary rates for strains from the Yamagata lineage were estimated as 3.82x10(-3) nucleotides/site/year and 2.62x10(-3) nucleotides/site/year for Victoria-related strains. In order to identify putative influenza B HA1 codons under selective pressure, a codon-substitution model for heterogeneous selective pressure at amino acid sites was used. A percentage of 97.3% of codons under negative selective pressure and 2.7% of codons under positive selective pressure (omega=dN/dS=2.65) were estimated, with posterior probability higher than 0.90. Amino acid sites 75, 197, and 199 were found more likely to be under positive selective pressure.
authors.affiliation: National Influenza Centre, Respiratory and Enterovirus Unit, National Institute of Health, Lisbon, Portugal.
authors.forename: Pedro
authors.initials: P
authors.lastname: Pechirra
authors.forename: Baltazar
authors.initials: B
authors.lastname: Nunes
authors.forename: Anabela
authors.initials: A
authors.lastname: Coelho
authors.forename: Carlos
authors.initials: C
authors.lastname: Ribeiro
authors.forename: Paulo
authors.initials: P
authors.lastname: Gonçalves
authors.forename: Sónia
authors.initials: S
authors.lastname: Pedro
authors.forename: Luísa Canto E
authors.initials: LC
authors.lastname: Castro
authors.forename: Helena
authors.initials: H
authors.lastname: Rebelo-de-Andrade
mesh_terms: D000940:Antigenic Variation / Q000235:genetics; D003062:Codon / Q000235:genetics; D019143:Evolution, Molecular; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000737:chemistry* / Q000235:genetics*; D006801:Humans; D009981:Influenza B virus / Q000145:classification / Q000235:genetics* / Q000276:immunology; D007251:Influenza, Human / Q000453:epidemiology / Q000635:transmission / Q000821:virology; D010802:Phylogeny; D012367:RNA, Viral / Q000235:genetics
chemical_list: D003062:Codon; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D012367:RNA, Viral