Functional significance of neuraminidase in the replication cycle of influenza viruses.

An influenza A strain with temperature sensitive neuraminidase was used for investigation of the functional significance of neuraminidase in different stages of the replication cycle. Heat inactivation of the neuraminidase does not diminish infectivity. Therefore, neuraminidase is not necessary for adsorption, penetration, and uncoating. At temperatures which inhibited neuraminidase activity there was also a reduction of intracellular haemagglutinin production but based on observations with a recombinant strain this was considered to be the consequence of a separate ts defect. Using quantitative haemadsorption to determine virus-dependent alteration of the cellular membrane no evidence was found that neuraminidase is involved in this process. However, release of haemagglutinin was considerably reduced if neuraminidase activity was diminished by temperature elevation. This function of the enzyme in the latest stage of the replication cycle can be substituted by V. cholerae neuraminidase.