EVOLUTION OF THE HEMAGGLUTININ GENE OF INFLUENZA-B VIRUS WAS DRIVEN BY BOTH POSITIVE AND NEGATIVE SELECTION PRESSURES

Nucleotide sequences of the hemagglutinin (HA) gene of twelve influenz a B strains and their deduced amino acid sequences were extracted from the GenBank and compared to those of early isolates. Separate analyse s of nonsynonymous and synonymous substitutions for the HA1 and HA2 re gions individually indicate that the percentage of nonsynonymous subst itutions in the HA1 ranges from 44.4-56.0% but in the HA2 from 0.0-6.5 %. The results suggest that positive selection as well as negative sel ection played a role in the evolution of the influenza B HA gene with the former acting on the HA1 and the latter on the HA2.