Hierarchical analysis of influenza A hemagglutinin gene sequences.

Five recently sequenced hemagglutinin genes from Influenza A virus strains are studied for similarities in a hierarchical fashion. The sequences are compared for similarity, first on the level of sequence homology, and then on several progressively more general levels. Though the HA1 subsequences contain regions where homology drops to that of a Monte Carlo generated reference value, subsequent tests reveal great similarity due to constraints on the level of amino acid sequence. Other tests detect statistically significant differences between subtypes due to constraints acting below the level of amino acid sequence, such as the 2 degrees structure of the viral RNA, or involving translation of the mRNA. The general applicability of the hierarchical approach to sequence analysis is discussed.