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Journal of Virology, December 1999, p. 9764-9772, Vol. 73, No. 12
Department of Microbiology and Program in
Molecular Biology, University of Iowa, Iowa City, Iowa 52242
Received 19 May 1999/Accepted 6 August 1999
In the NL4-3 strain of human immunodeficiency virus type 1 (HIV-1),
regulatory elements responsible for the relative efficiencies of
alternative splicing at the tat, rev, and the
env/nef 3' splice sites (A3 through A5) are contained
within the region of tat exon 2 and its flanking sequences.
Two elements affecting splicing of tat, rev,
and env/nef mRNAs have been localized to this region. First, an exon splicing silencer (ESS2) in NL4-3, located approximately 70 nucleotides downstream from the 3' splice site used to generate tat mRNA, acts specifically to inhibit splicing at this
splice site. Second, the A4b 3' splice site, which is the most
downstream of the three rev 3' splice sites, also serves as
an element inhibiting splicing at the env/nef 3' splice
site A5. These elements are conserved in some but not all HIV-1
strains, and the effects of these sequence changes on splicing have
been investigated in cell transfection and in vitro splicing assays.
SF2, another clade B virus and member of the major (group M) viruses,
has several sequence changes within ESS2 and uses a different
rev 3' splice site. However, splicing is inhibited by the
two elements similarly to NL4-3. As with the NL4-3 strain, the SF2 A4b
AG dinucleotide overlaps an A5 branchpoint, and thus the inhibitory
effect may result from competition of the same site for two different
splicing factors. The sequence changes in ANT70C, a member of the
highly divergent outlier (group O) viruses, are more extensive, and
ESS2 activity in tat exon 2 is not present. Group O viruses
also lack the rev 3' splice site A4b, which is conserved in
all group M viruses. Mutagenesis of the most downstream rev
3' splice site of ANT70C does not increase splicing at A5, and all of
the branchpoints are upstream of the two rev 3' splice
sites. Thus, splicing regulatory elements in tat exon 2 which are characteristic of most group M HIV-1 strains are not present
in group O HIV-1 strains.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Splicing Regulatory Elements within tat Exon 2 of
Human Immunodeficiency Virus Type 1 (HIV-1) Are Characteristic of
Group M but Not Group O HIV-1 Strains
*
Corresponding author. Mailing address: Department of
Microbiology and Program in Molecular Biology, University of Iowa, Iowa City, IA 52242. Phone: (319) 335-7793. Fax: (319) 335-9006. E-mail: marty-stoltzfus{at}uiowa.edu.
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