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J. Virol., Mar 1997, 2138-2145, Vol 71, No. 3
T Odagiri and M Tashiro
The generation of influenza A virus defective interfering (DI) particles
was studied by using an NS2 mutant which produces, in a single cycle of
virus replication, a large amount of DI particles lacking the PA polymerase
gene. The decrease in PA gene replication has been shown to occur primarily
at the cRNA synthesis step, with preferential amplification of PA DI RNA
species present in a marginal amount in the virus stock. In addition, at
the assembly step the PA DI RNAs were preferentially incorporated into
virions, resulting in selective reduction in the packaging of the PA gene
into virions. Similarly, in cells dually infected with the NS2 mutant and
wild-type viruses, packaging of the wild-type PA gene was also greatly
suppressed. In contrast, incorporation of other RNA segments, i.e., the PB2
and NS genes, was not affected, suggesting that the PA DI RNAs competed
only with the PA gene in a segment-specific manner. Experiments involving
rescue of recombinant chloramphenicol acetyltransferase (CAT) RNA flanked
by the noncoding regions of the PA (PA/CAT RNA) and PB2 (PB2/CAT RNA) genes
into viral particles showed that only PA/CAT RNA was not rescued by
infection with the NS2 mutant virus containing the PA DI RNAs. However,
recombinant PA/CAT RNA in which either the 3' or 5' noncoding region was
replaced with that of the PB2 gene was rescued by the NS2 mutant. These
results suggest that the noncoding regions of the PA gene are responsible
for the competition with PA DI RNA species at the virus assembly step and
that coexistence of the both noncoding regions would be a prerequisite for
this phenomenon. Decreased packaging of the progenitor RNA by the DI RNA,
in addition to the suppression of cRNA synthesis, is likely involved in the
production of DI particles.
Copyright © 1997, American Society for Microbiology
Segment-specific noncoding sequences of the influenza virus genome RNA are involved in the specific competition between defective interfering RNA and its progenitor RNA segment at the virion assembly step
Department of Virology, Jichi Medical School, Minami-Kawachi, Tochigi, Japan. todagiri@jichi.ac.jp
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