[2 forms of influenza virus nucleocapsid protein (NP) in virions and infected cells].

Two forms of the major nucleocapsid protein (NP) of influenza virus were found which an polyacrylamide gel electrophoresis had the mobility corresponding to those of proteins with moleculr weights of 56,000 (NP56) and 53,000 (NP53) daltons. A pulse-chase experiment showed the NP53 polypeptide to be a transformation product of NP56 polypeptide. Peptide mapping indicated that both proteins were quite similar, except that NP56 had two additional peptides suggesting the mechanism of NP53 derivation from NP56 by cleavage of a small peptide (molecular weight about 3000 daltons). Both classes of NP protein molecules were found both in infected cells and in virions. The intensity of intracellular modification NP56 leads to NP53 was dissimilar in different cell lines and practically did not depend on the virus strain. In virus preparations obtained from different cells in NP53 protein content varied but this polypeptide was always found as a minor component. In the infected cells the ratio of NP53 to NP56 polypeptides was significantly higher than in virions indicating the preferable incorporation into the virus progeny of polypeptides with intact NP56 protein.