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J. Virol., 07 1996, 4370-4379, Vol 70, No. 7
S Mahajan, VV Dolja and JC Carrington
The roles of the capsid protein (CP) and the CP coding sequence of tobacco
etch potyvirus (TEV) in genome amplification were analyzed. A series of
frameshift-stop codon mutations that interrupted translation of the CP
coding sequence at various positions were introduced into the TEV genome. A
series of 3' deletion mutants that lacked the CP coding sequence beyond
each of the frameshift-stop codon mutations were also produced. In
addition, a series of 5' CP deletion mutants were generated. Amplification
of genomes containing either frameshift-stop codon insertions after codons
1, 59, 103, and 138 or genomes containing the corresponding 3' deletions of
the CP coding sequence was reduced by 100- to 1,000-fold relative to that
of the parental genome in inoculated protoplasts. In contrast, a mutant
containing a frameshift- stop codon after CP position 189 was amplified to
27% of the level of the parental virus, but the corresponding 3' deletion
mutant lacking codons 190 to 261 was nonviable. Deletion mutants lacking CP
codons 2 to 100, 2 to 150, 2 to 189, and 2 to 210 were amplified relatively
efficiently in protoplasts, but a deletion mutant lacking codons 2 to 230
was nonviable. None of the amplification-defective frameshift-stop codon or
deletion mutants was rescued in transgenic cells expressing TEV CP,
although the transgenic CP was able to rescue intercellular movement
defects of replication-competent CP mutants. Coupled with previous results,
these data led to the conclusions that (i) TEV genome amplification
requires translation to a position between CP codons 138 and 189 but does
not require the CP product and (ii) the TEV CP coding sequence contains a
cis-active RNA element between codons 211 and 246. The implications of
these findings on mechanisms of RNA replication and genome evolution are
discussed.
Copyright © 1996, American Society for Microbiology
Roles of the sequence encoding tobacco etch virus capsid protein in genome amplification: requirements for the translation process and a cis-active element
Department of Biology, Texas A&M University, College Station, Texas 77843-3258, USA.
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