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J. Virol., Mar 1996, 1406-1414, Vol 70, No. 3
H Jin, K Subbarao, S Bagai, GP Leser, BR Murphy and RA Lamb
The C terminus of the influenza virus hemagglutinin (HA) contains three
cysteine residues that are highly conserved among HA subtypes, two in the
cytoplasmic tail and one in the transmembrane domain. All of these
C-terminal cysteine residues are modified by the covalent addition of
palmitic acid through a thio-ether linkage. To investigate the role of HA
palmitylation in virus assembly, we used reverse genetics technique to
introduce substitutions and deletions that affected the three conserved
cysteine residues into the H3 subtype HA. The rescued viruses contained the
HA of subtype H3 (A/Udorn/72) in a subtype H1 helper virus (A/WSN/33)
background. Rescued viruses which do not contain a site for palmitylation
(by residue substitution or substitution combined with deletion of the
cytoplasmic tail) were obtained. Rescued virions had a normal polypeptide
composition. Analysis of the kinetics of HA low-pH-induced fusion of the
mutants showed no major change from that of virus with wild-type (wt) HA.
The PFU/HA ratio of the rescued viruses grown in eggs ranged from that of
virus with wt HA to 16-fold lower levels, whereas the PFU/HA ratio of the
rescued viruses grown in MDCK cells varied only 2-fold from that of virus
with wt HA. However, except for one rescued mutant virus (CAC), the mutant
viruses were attenuated in mice, as indicated by a > or = 400-fold
increase in the 50% lethal dose. Interestingly, except for one mutant virus
(CAC), all of the rescued mutant viruses were restricted for replication in
the upper respiratory tract but much less restricted in the lungs. Thus,
the HA cytoplasmic tail may play a very important role in the generation of
virus that can replicate in multiple cell types.
Copyright © 1996, American Society for Microbiology
Palmitylation of the influenza virus hemagglutinin (H3) is not essential for virus assembly or infectivity
Howard Hughes Medical Institute, Northwestern University, Evanston, Illinois 60208-3500, USA.
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