THE ECTODOMAINS BUT NOT THE TRANSMEMBRANE DOMAINS OF THE FUSION PROTEINS OF SUBTYPE-A AND SUBTYPE-B AVIAN PNEUMOVIRUS ARE CONSERVED TO A SIMILAR EXTENT AS THOSE OF HUMAN RESPIRATORY SYNCYTIAL VIRUS

The fusion glycoprotein (F-B) gene of five strains of the B subtype of avian pneumovirus (APV; turkey rhinotracheitis virus) has been sequen ced. The length of the F-B protein was 538 amino acids, identical to t hat of the F protein of subtype A virus, with which it had 74% and 83% overall nucleotide and! deduced amino acid identities, respectively. The: F-B and F-A ectodomains had 90% amino acid identity, very similar to the 91% identity between the ectodomains of the F proteins of subt ype A and B human respiratory syncytial virus (HRSV), As with HRSV, th e F2 polypeptide was less conserved (83% identity) than F1 (94%), In c ontrast to the ectodomain, the transmembrane and cytoplasmic domains o f the two APV subtypes were much less conserved (30% and 48% identity, respectively) than those of HRSV (92% and 87%, respectively). Compari sons within all the genera of the Paramyxoviridae (Pneumovirus, Morbil livirus, Paramyxovirus and Rubullavirus) show that low amino acid iden tity between F protein transmembrane domains is a feature of different species of virus rather than of strain differences. This may indicate that the two subtypes of APV have evolved in different geographical r egions and/or different avian species. This is the first report of an F gene sequence from a subtype B APV.