The M2 protein of influenza A virus functions as an ion channel. It co
ntains three cysteine residues: cysteines 17 and 19, which form disulf
ide bonds in the ectodomain, and cysteine 50, which is acylated. To un
derstand the role of these cysteine residues in virus replication, we
used reverse genetics to create influenza viruses in which the individ
ual cysteines were mutated and a virus in which all three cysteines we
re changed to serine. The M2 cysteine mutants that lacked either of th
e cysteine residues in the ectodomain and the mutant that lacked all t
hree residues had appreciably lower amounts of M2 oligomers than did t
he wild-type virus when examined by sodium dodecyl sulfate-polyacrylam
ide gel electrophoresis. None of the mutants, however, were defective
in replication, either in vitro or in ferrets and mice; These findings
demonstrate that noncovalent interactions are sufficient for the M2 p
rotein to form functional oligomers for virus replication and that its
cysteine residues are dispensable for influenza virus replication in
vitro and in vivo. (C) 1997 Academic Press.