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Journal of Virology, June 1999, p. 4941-4951, Vol. 73, No. 6
Department of Microbiology and Immunology,
The University of Texas Medical Branch at Galveston, Galveston,
Texas 77555-10191; First Department of
Internal Medicine, Kanazawa University, Kanazawa,
Japan2; and Department of Surgery, The
University of North Carolina at Chapel Hill, Chapel Hill, North
Carolina 275993
Received 16 September 1998/Accepted 4 March 1999
The 5' nontranslated RNA (5'NTR) of a genotype 1b hepatitis C virus
(HCV-N) directs cap-independent translation of the HCV-N polyprotein
with about twofold less efficiency than the 5'NTR of a genotype 1a
virus under physiologic conditions (Hutchinson strain, or HCV-H)
(M. Honda et al., Virology 222:31-42, 1996). Here,
we show by mutational analysis that substitution of the AG
dinucleotide sequence at nucleotides (nt) 34 and 35 of HCV-N with GA
(present in HCV-H) restores the translational activity to that of the
HCV-H 5'NTR both in vitro and in vivo. These nucleotides are located
upstream of the minimal essential internal ribosome entry site
(IRES), as a 6-nt deletion spanning nt 32 to 37 also increased the
translational activity of the HCV-N 5'NTR to that of HCV-H.
Thus, the upstream AG dinucleotide sequence has an inhibitory effect on
IRES-directed translation. Surprisingly, however, this inhibitory effect was observed only when the translated, downstream RNA sequence contained nt 408 to 929 of HCV (capsid-coding RNA). Further analysis of RNA transcripts containing frameshift mutations demonstrated that the nucleotide sequence of the transcript, and not
the amino acid sequence of the expressed capsid protein, determines this difference in translation efficiency. The difference
between the translational activities of the HCV-N and HCV-H
transcripts was increased when translation was
carried out in reticulocyte lysates containing high
K+ concentrations, with a sevenfold difference evident
at 130 to 150 mM K+. These results suggest
that there is an RNA-RNA interaction involving 5'NTR and
capsid-coding sequences flanking the IRES and that
this is responsible for the reduced IRES activity of the genotype 1b virus, HCV-N.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Natural Variation in Translational Activities of the 5'
Nontranslated RNAs of Hepatitis C Virus Genotypes 1a and 1b: Evidence
for a Long-Range RNA-RNA Interaction outside of the Internal
Ribosomal Entry Site
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, The University of Texas Medical Branch at Galveston, 301 University Blvd., Galveston, TX 77555-1019. Phone: (409)
772-2324. Fax: (409) 772-3757. E-mail: smlemon{at}utmb.edu.
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