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J. Virol., 01 1996, 241-247, Vol 70, No. 1
K Watanabe, H Handa, K Mizumoto and K Nagata
Influenza virus M1 protein has been shown to inhibit the transcription
catalyzed by viral ribonucleoprotein complexes isolated from virions. Here,
this inhibition mechanism was studied with the recombinant M1 protein
purified from Escherichia coli expressing it from cDNA. RNA mobility shift
assays indicated that both soluble and aggregate forms of the recombinant
M1, which were separated by the glycerol density gradient, were bound to
RNA. Once an M1-RNA complex was formed, free M1 was bound to the M1-RNA
complex cooperatively rather than to free RNA. In addition, the recombinant
M1 was capable of binding to preformed RNA- nucleocapsid protein complexes.
The mechanism for inhibition of the viral RNA polymerase activity was
analyzed by the in vitro RNA synthesis systems that depend on an
exogenously added RNA template. These systems were more sensitive for
evaluating the inhibition by M1 than the RNA synthesis system depending on
an endogenous RNA template. The RNA synthesis inhibition was examined at
four steps: cleavage of capped RNA; incorporation of the first nucleotide,
GMP; limited elongation; and synthesis of full-size product. M1 inhibited
RNA synthesis mainly at the early steps. The experiments with M1 mutant
proteins containing amino acid deletions suggested that the M1 region
between amino acid residues 91 and 111 was essential for anti-RNA synthesis
activity, RNA binding, and oligomerization of M1 on RNA.
Copyright © 1996, American Society for Microbiology
Mechanism for inhibition of influenza virus RNA polymerase activity by matrix protein
Tokyo Institute of Technology, Yokohama, Japan.
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