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J. Virol., Mar 1997, 2050-2058, Vol 71, No. 3
MS McBride and AT Panganiban
At least two hairpins in the 5' untranslated leader region, stem-loops 1
and 3 (SL1 and SL3), contribute to human immunodeficiency virus type 1 RNA
encapsidation in vivo. We used a competitive assay, which measures the
relative encapsidation efficiency of mutant viral RNA in the presence of
competing wild-type RNA, to compare the contributions of SL1, SL3, and two
adjacent secondary structures, SL2 and SL4, to encapsidation. SL2 is not
required for RNA encapsidation, while SL1, SL3, and SL4 all contribute
approximately equally to encapsidation. To determine whether these hairpins
function in a position-dependent manner, we interchanged the positions of
two of these stem-loop structures. This resulted in substantial diminution
of encapsidation, indicating that the secondary structures that comprise E,
the encapsidation signal, function only in their correct contexts. Mutation
of nucleotides flanking SL1 and SL3 had little effect on encapsidation. We
also showed that SL1, while present on both genomic and subgenomic viral
RNAs, nonetheless contributes to selective encapsidation of genomic RNA.
Taken together, these data are consistent with the formation of a
higher-order RNA structure, partially composed of SL1, SL3, and SL4, that
functions to effect concurrent encapsidation of full- length RNA and
exclusion of subgenomic RNA. Finally, it has been reported that E is
required for efficient translation of Gag mRNA in vivo. However, we have
found that a variety of mutants, including a mutant lacking the entire
region encompassing SL1, SL2, and SL3, still produce RNAs that are
efficiently translated. These data indicate that E is unlikely to
contribute to efficient Gag mRNA translation in vivo.
Copyright © 1997, American Society for Microbiology
Position dependence of functional hairpins important for human immunodeficiency virus type 1 RNA encapsidation in vivo
McArdle Laboratory for Cancer Research, University of Wisconsin Medical School, Madison 53706, USA.
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