PRECURSOR GLYCOPROTEIN IN INFLUENZA-C VIRUS

Influenza C virions grown in chicken kidney cells contain two glycoprotein size classes when analyzed under nonreducing conditions. These are designated gpI and gpII, with molecular weights of ∼105,000 and ∼82,000, respectively. We have obtained evidence that these glycoproteins share common amino acid sequences, and that gpI is the primary viral gene product which may be converted into gpII by proteolytic cleavage. When analyzed under reducing conditions, gpI was observed as a single, uncleaved polypeptide chain, whereas gpII was found to consist of two subunits with molecular weights of ∼65,000 and 30,000 respectively. Influenza C virus preparations grown in different host cells varied in the extent of cleavage of gpI into gpII. Virions grown in chick embryo fibroblast (CEF) cells contained exclusively gpI, whereas egg-grown virions possessed predominantly gpII glycoproteins. Treatment of CEF-grown virions with trypsin converted gpI into gpII; the specific infectivity of such preparations was increased up to 50-fold by trypsin treatment. These results indicate that cleavage of gpI into gpII is essential for maximal viral infectivity. © 1979.