Isolation and characterization of the measles virus F1 polypeptide: comparison with other paramyxovirus fusion proteins.

Measles virus fusion (F) protein has been isolated by immunoadsorption to a complex of monoclonal antibodies bound to protein A-Sepharose. The 41-kDa F1 component of the fusion protein was obtained pure in high yield by preparative SDS-polyacrylamide gel electrophoresis. The amino acid composition of the F1 chain was determined and the N-terminal sequence was analyzed for 40 residues. The structure determined is largely hydrophobic, with 24 residues of Val, Ile, Leu, Met, Phe, or Ala. Comparison with previously published data on the F1 polypeptide of Sendai virus showed considerable similarity in amino acid composition. Extensive N-terminal sequence homologies with F1 polypeptides of different paramyxoviruses are also noticed, including a nine-residue segment strictly conserved among four F1 polypeptides studied, as well as a weaker but distinct and Gly-rich sequence homology with the influenza A and B virus HA2 polypeptides. The evolutionary conservation of the N-terminal region at the site of cleavage of surface glycoproteins of the two families of myxoviruses highlights its specialized function in membrane fusion.