Adaptive evolution on HA1 subunit of influenza B virus

Abstract

Some studies on the influenza AH3 viruses showed that a small number of codons in the HA1 had been under positive selection. However, the existence of amino acid sites under positive selective pressure in the influenza B HA1 subunit has not been a major issue of study. In this work it was used as the parameter, ω= d N/ d S (acceptance rate of non-synonymous substitutions), to test the hypothesis of the existence of adaptive evolution on the HA1 subunit of influenza B and identify the codons more likely to be under positive selective pressure. The data were related to 80 HA1 segments of the haemagglutinin gene of influenza B virus. For the sequence analysis, codon-substitution models for heterogeneous selective pressure at amino acid sites were used. The maximum likelihood estimates were obtained (package PAML 3.13a) for the models referred to as M0 to M8 [Genetics, 155 (2000) 431]. The model with better results was the M3, estimating a percentage of 97.4% of the codon under negative selective pressure (65.9% with ω<0.0001; 31.4% with ω=0.465), and 2.6% of the codon under positive selective pressure with ω=2.65. The sites 75, 197 and 199 were more likely to be under positive selective pressure, with posterior probability superior to 0.90. From those three amino acids, two (sites 197 and 199) form a potential N-glycosilation site.