title: Influenza C virus hemagglutinin: comparison with influenza A and B virus hemagglutinins.
abstract: The complete nucleotide sequence of the influenza C/California/78 virus RNA 4 was obtained by using cloned cDNA derived from the RNA segment. This gene is 2,071 nucleotides long and can code for a polypeptide of 654 amino acids. Although there are no convincing sequence homologies between RNA 4 and the hemagglutinin genes of influenza A and B viruses, we suggest, on the basis of structural features, that RNA 4 of the influenza C virus codes for the hemagglutinin. The structural features which are common to the hemagglutinins of influenza A, B, and C viruses include (i) a hydrophobic signal peptide, (ii) an arginine cleavage site between the hemagglutinin 1 and 2 subunits, (iii) hydrophobic regions at the amino and carboxyl termini of the hemagglutinin 2 subunit, and (iv) several conserved cysteine residues. Additional evidence that RNA 4 of influenza C virus codes for the hemagglutinin is that the tripeptide Ile-Phe-Gly, known to be present at the amino terminus of the hemagglutinin 2 subunit of influenza C virus, is encoded by RNA 4 at a point immediately adjacent to the presumptive arginine cleavage site. The lack of primary sequence homology between the influenza C virus hemagglutinin and the influenza A or B virus hemagglutinins, which all have similar functions, might be attributed to convergent rather than divergent evolution. However, the structural similarities among the influenza A, B, and C virus hemagglutinins strongly suggest that the three hemagglutinin genes have diverged from a common precursor.
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D005075:Biological Evolution; D003545:Cysteine / Q000032:analysis; D005814:Genes, Viral; D006389:Hemagglutinins, Viral / Q000032:analysis / Q000235:genetics*; D009980:Influenza A virus / Q000235:genetics / Q000276:immunology*; D009975:Orthomyxoviridae / Q000235:genetics / Q000276:immunology*; D010455:Peptides / Q000032:analysis; D021382:Protein Sorting Signals; D012367:RNA, Viral / Q000235:genetics*; D012794:Sialic Acids / Q000378:metabolism
chemical_list: D006389:Hemagglutinins, Viral; D010455:Peptides; D021382:Protein Sorting Signals; D012367:RNA, Viral; D012794:Sialic Acids; D003545:Cysteine