The cytoplasmic tails of the influenza virus spike glycoproteins are required for normal genome packaging

Deletion of the cytoplasmic tails of the influenza A virus spike glycoprote ins, hemagglutinin (HA) and neuraminidase (NA), has previously been shown t o result in markedly defective virion morphogenesis (Jin et al, 1997, EMBO J. 16, 1236-1247). we have found that influenza A virus preparations lackin g the HA and NA cytoplasmic tails (HAt-/NAt-) have a reduced vRNA to protei n content, contain an increase in cellular RNA contaminants, and exhibit in creased resistance to ultraviolet (UV) inactivation. There is also a direct correlation between abnormal virion morphology and reduced infectivity. Th e data suggest that the HAt-/NAt- virion population contains a broader rang e of number of packaged RNA segments than wild-type (wt) virus. Sucrose gra dient centrifugation analysis indicated the presence of a subpopulation of virions with pronounced deformation in virion morphology and reduced infect ivity. The role of the HA and NA cytoplasmic tails was examined further by using a trans-complementation assay and it was found that expression of wt HA and NA from cDNAs followed by HAt-/NAt- virus infection caused the forma tion of a pseudotype virus with wt sedimentation properties. Taken together the data indicate that the HA and NA cytoplasmic tails affect not only vir ion morphology but also proper genome packaging. (C) 2000 Academic Press.