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J. Virol., Jul 1996, 4667-4682, Vol 70, No. 7
E Berthold and F Maldarelli
Two distinct intranuclear locations were identified for alternatively
spliced RNA transcripts expressed from the pNL4-3 infectious molecular
clone of human immunodeficiency virus (HIV) type 1. Multiply spliced HIV
RNA encoding tat was detected within the nucleus in large clusters;
immunostaining and colocalization studies using laser-scanning confocal
microscopy revealed that these structures contained the non-small nuclear
ribonucleoprotein RNA processing factor, SC35. In contrast, unspliced gag
RNA was detected in much smaller granules distributed throughout the
nucleus, with little or no association with SC35- containing granules.
Analyses of nuclear RNA expressed from recombinant plasmids encoding gag
(pCMVgag-2) alone or tat (pCMVtat-2) alone revealed distributions
corresponding to those obtained with pNL4-3, indicating that expression
within the context of the HIV provirus was not required for the distinct
RNA locations detected for these transcripts. The presence of unspliced gag
RNA in small granules was confirmed in infections of H9 T-lymphocytic
cells, indicating that gag localization was not restricted to transient
expression systems. The intranuclear distribution of gag RNA was dependent
on specific RNA sequences. Deletion of a portion of the gag gene of
pCMVgag-2, containing a cis-repressing inhibitory region, resulted in
redirection of unspliced gag RNA from small granules into large
SC35-containing clusters. The addition of the Rev-responsive element, RRE,
to the deleted pCMVgag-2 construct resulted in RNA transcripts which were
no longer associated with SC35. We also identified a cellular intron,
rabbit beta-globin-intervening sequence 2 (IVS-2) which, when introduced
into pCMVgag-2, redirected unspliced gag RNA into SC35- containing granules
and permitted rev-independent Gag expression. These findings suggest that
redirecting intranuclear RNA localization may influence gene expression.
Color micrographs from this article are available for view at
http//128.231.216.2/lmmhome.htm.
Copyright © 1996, American Society for Microbiology
cis-acting elements in human immunodeficiency virus type 1 RNAs direct viral transcripts to distinct intranuclear locations
Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892, USA.
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