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Journal of Virology, December 2000, p. 11581-11588, Vol. 74, No. 24
LaboRétro, Unité de Virologie
Humaine, Institut National de la Santé et de la Recherche
Médicale, Ecole Normale Supérieure de Lyon, 69364 Lyon
Cedex 07, France
Received 24 May 2000/Accepted 25 September 2000
The 5' leader of Rous sarcoma virus (RSV) genomic RNA and of
retroviruses in general is long and contains stable secondary structures that are critical in the early and late steps of virus replication such as RNA dimerization and packaging and in the process
of reverse transcription. The initiation of RSV Gag translation has
been reported to be 5' cap dependent and controlled by three short open
reading frames located in the 380-nucleotide leader upstream of the Gag
start codon. Translation of RSV Gag would thus differ from that
prevailing in other retroviruses such as murine leukemia virus,
reticuloendotheliosis virus type A, and simian immunodeficiency virus,
in which an internal ribosome entry segment (IRES) in the 5' end of the
genomic RNA directs efficient Gag expression despite stable 5'
secondary structures. This prompted us to investigate whether RSV Gag
translation might be controlled by an IRES-dependent mechanism. The
results show that the 5' leaders of RSV and v-Src RNA exhibit IRES
properties, since these viral elements can promote efficient
translation of monocistronic RNAs in conditions inhibiting 5'
cap-dependent translation. When inserted between two cistrons in a
canonical bicistronic construct, both the RSV and v-Src leaders promote
expression of the 3' cistron. A genetic analysis of the RSV leader
allowed the identification of two nonoverlapping 5' and 3' leader
domains with IRES activity. In addition, the v-Src leader was found to
contain unique 3' sequences promoting an efficient reinitiation of
translation. Taken together, these data lead us to propose a new model
for RSV translation.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Rous Sarcoma Virus Translation Revisited:
Characterization of an Internal Ribosome Entry Segment in the 5' Leader
of the Genomic RNA
*
Corresponding author. Mailing address: LaboRétro,
Unité de Virologie Humaine #412, Institut National de la
Santé et de la Recherche Médicale, Ecole Normale
Supérieure de Lyon, 46 Allée d' Italie, 69364 Lyon Cedex
07, France. Phone: 33-472-72-81-69. Fax: 33-472-72-86-86. E-mail:
Jean-Luc.Darlix{at}ens-lyon.fr.
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