J Virol, May 1998, p. 3907-3915, Vol. 72, No. 5
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Lady Davis Institute for Medical Research and
McGill AIDS Centre,
Received 1 July 1997/Accepted 15 January 1998
We have studied the effect of mutations in the human
immunodeficiency virus type 1 (HIV-1) nucleocapsid (NC) sequence on
tRNA3Lys genomic placement, i.e., the in vivo placement
of primer tRNA3Lys on the HIV-1 primer binding site
(PBS). HIV-1 produced from COS cells transfected with wild-type or
mutant proviral DNA was used in this study. We have found that
mutations in the amino acid sequences flanking the first Cys-His box in
the NC sequence produce the maximum inhibition of genomic placement. A
similar finding was obtained when the NC-facilitated annealing of
primer tRNA3Lys to the HIV PBS in vitro was studied.
However, since the genomic placement of tRNA3Lys occurs
independently of precursor protein processing, the NC mutations studied
here have probably exerted their effect through one or both of the
precursor proteins, Pr55gag and/or
Pr160gag-pol. One mutation in the linker region
between the two Cys-His boxes, P31L, prevented packaging of both
Pr160gag-pol and tRNA3Lys and
prevented the genomic placement of tRNA3Lys. Both
packaging and genomic placement were rescued by cotransfection with a
plasmid coding for wild-type Pr160gag-pol. For
other linker mutations [R7R10K11 S, R32G, and S3(32-34)], packaging
of Pr160gag-pol and tRNA3Lys
was not affected, but genomic placement was, and placement could not be
rescued by cotransfection with plasmids coding for either Pr55gag or
Pr160gag-pol. After placement, the initiation
of reverse transcription within extracellular virions is characterized
by a 2-base DNA extension of the placed tRNA3Lys. This
process requires precursor processing, and those NC mutations which
showed the most inhibition of initiation were in either of the two NC
Cys-His boxes. Destabilization of a U5 stem-A-rich loop immediately
upstream of the PBS (through deletion of four consecutive A's in the
loop) did not affect the in vivo genomic placement of
tRNA3Lys but resulted in the presence in the
extracellular virus of longer cDNA extensions of
tRNA3Lys, with a corresponding decrease in the presence
of unextended and 2-base-extended tRNA3Lys.
*
Corresponding author. Mailing address: Lady Davis
Institute for Medical Research, Jewish General Hospital, 3755 Cote
Ste-Catherine Rd., Montreal, Quebec H3T 1E2, Canada. Phone: (514)
340-8260. Fax: (514) 340-7502. E-mail:
md26{at}musica.mcgill.ca.
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