Influenza virus hemagglutinin containing an altered hydrophobic carboxy terminus accumulates intracellularly.

The influenza virus hemagglutinin (HA) glycoprotein synthesized from cloned DNA in a simian virus 40 vector is expressed on the surface of infected primate cells. Previously, it has been demonstrated that mutant HAs lacking the hydrophobic carboxy terminus fail to anchor on the cell surface and therefore are secreted extracellularly. During analysis of additional HA deletion mutants derived from an HA-simian virus 40 recombinant, we found a mutant with an altered hydrophobic carboxy terminus that exhibited another phenotype. This deletion mutant, dl-12, produced HA that was neither secreted nor expressed on the infected cell surface. The mutant HA was similar to the wild-type HA in apparent molecular weight and extent of glycosylation as assayed by endoglycosidase H sensitivity. The mutant HA localized near the perinuclear region of infected cells as indicated by an indirect immunofluorescence assay. Sequence analysis showed that a 5-base-pair deletion had occurred before the region encoding the hydrophobic carboxy terminus. Nevertheless, the physicochemical properties of the wild-type HA carboxy terminus were maintained in that the truncated HA carboxy terminus consisted of predominantly hydrophobic amino acids followed by several charged amino acids residues. This similarity in the carboxy terminus between the wild-type and mutant HAs may be responsible for the functional similarities observed. In spite of these similarities, the mutant HA failed to mature at the surface. These results suggest that the maturation of the mutant HA is blocked during a late stage in the transit to the cell surface.