Nucleotide and deduced amino acid sequence of hemagglutinin-neuraminidase genes of human type 3 parainfluenza viruses isolated from 1957 to 1983.

We have sequenced the coding and noncoding regions of the hemagglutinin-neuraminidase (HN) genes of six clinical strains of human type 3 parainfluenza virus (PIV3) isolated between 1973 and 1983, and compared them to the prototype 1957 strain. Sequence variability does not result from the accumulation of mutations over time, but represents genetic heterogeneity in HN genes within the PIV3 population. Most of the nucleotide diversity occurs in the 5' noncoding sequences, exclusive of regions supplying transcriptional and translational control elements. Although the overall amino acid homology among HN proteins is very high, most variability is concentrated in domains at the carboxyl and amino terminus. This uneven distribution of amino acid diversity may reflect both functional and structural constraints on different HN domains and the epidemiologic features of PIV3 infection.