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Query: UMLS:C0021051 (immunodeficiency)
 71,517 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The TAR element extending from -17 to +80 in the human immunodeficiency virus long terminal repeat (HIV LTR) is required for activation of gene expression by the tat trans-activator protein. TAR RNA forms a stable stem-loop structure, and mutagenesis studies indicate that the stem structure, the primary sequence of the loop, and the bulge element are the major determinants for tat activation. RNA gel retardation analysis demonstrates that both tat and cellular proteins bind to TAR RNA, but the mechanism by which these proteins increase HIV gene expression is unknown. We have fractionated HeLa cell nuclear extracts in an attempt to identify cellular proteins that bind to TAR RNA and are involved in regulating HIV gene expression. RNA gel retardation and UV cross-linking reveal that a cellular protein of 185 kD, which we designate TAR RNA-binding protein 185 (TRP-185), binds with both high affinity and marked specificity to TAR RNA. RNA gel retardation and competition analyses indicate that TRP-185 binding is strongly dependent on the TAR RNA loop sequences. The binding of TRP-185 is modulated by both a set of cellular cofactors and the tat protein. Highly purified preparations of TRP-185 are capable of activating in vitro transcription of wild-type, but not mutated, HIV LTR chloramphenicol acetyltransferase (CAT) constructs. These results characterize a positively acting cellular RNA-binding factor, TRP-185, which is involved in the regulation of HIV gene expression.
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PMID:tat regulates binding of the human immunodeficiency virus trans-activating region RNA loop-binding protein TRP-185. 193 97

All human immunodeficiency virus mRNAs contain a sequence known as TAR (trans-activating responsive sequence). The TAR element forms a stable RNA stem-loop structure which binds the HIV tat (trans-activator) protein and mediates increased viral gene expression. In principle, molecules which bind to the TAR RNA structure would inhibit trans-activation by perturbing the native RNA secondary structure. We have constructed a series of phosphodiester and phosphorothioate antisense oligonucleotides which specifically bind to the HIV TAR element. Specific binding to the TAR element was demonstrated in vitro with enzymatically synthesized TAR RNA. The TAR-directed phosphorothioates inhibited trans-activation in a sequence-dependent fashion in a cell culture model using an HIV LTR/human placental alkaline phosphatase gene fusion and tat protein supplied in trans. The molecules also inhibited HIV replication in both acute and chronically infected viral assays, but without sequence specificity. We have constructed a series of vectors consisting of the MMTV promoter and 5'-untranslated region of four different mRNAs, including the TAR region, to study the effect of TAR on gene expression in heterologous systems. The results suggest that, in the absence of the HIV LTR, the TAR element has a repressive effect on gene expression, which is relieved by tat.
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PMID:Inhibition of HIV-LTR gene expression by oligonucleotides targeted to the TAR element. 206 53

The basic domain of Tat is required for trans-activation of viral gene expression. We have performed scanning peptide studies to demonstrate that only this domain is capable of binding to the TAR RNA stem-loop. Strikingly, the basic domain of the other human immunodeficiency virus trans-acting factor, Rev, but no other region, is also capable of binding to TAR. Peptide derivatives of Tat do not require the highly conserved glutamine residue at position 54 for TAR binding, since it may be substituted or deleted. In addition, the two lysine residues may be replaced by arginines. Analysis of binding and trans-activation demonstrated that homopolymers of arginine can completely substitute for the basic domain. Such homopolymers have high affinity for wild-type TAR RNA and lower affinity for mutant TAR. Homopolymers of six to nine arginines substituting for the basic domain of Tat enable full trans-activation in vivo. Homopolymers of at least seven arginines are required for detectable in vitro complex formation, although approximately 30% trans-activation is achieved with a mutant Tat containing only five arginines.
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PMID:The number of positively charged amino acids in the basic domain of Tat is critical for trans-activation and complex formation with TAR RNA. 206 4

Multiple regulatory elements in the human immunodeficiency virus long terminal repeat (HIV LTR) are required for activation of HIV gene expression. Previous transfection studies of HIV LTR constructs linked to the chloramphenicol acetyltransferase gene indicated that multiple regulatory regions including the enhancer, SP1, TATA and TAR regions were important for HIV gene expression. To characterize these regulatory elements further, mutations in these regions were inserted into both the 5' and 3' HIV LTRs and infectious proviral constructs were assembled. These constructs were transfected into either HeLa cells, Jurkat cells or U937 cells in both the presence and absence of phorbol esters which have previously been demonstrated to activate HIV gene expression. Viral gene expression was assayed by the level of p24 gag protein released from cultures transfected with the proviral constructs. Results in all cell lines indicated that mutations of the SP1, TATA and the TAR loop and stem secondary structure resulted in marked decreases in gene expression while mutations of the enhancer motif or TAR primary sequence resulted in only slight decreases. However, viruses containing mutations in either the TAR loop sequences or stem secondary structure which were very defective for gene expression in untreated Jurkat cells, gave nearly wild-type levels of gene expression in phorbol ester-treated Jurkat cells but not in phorbol ester-treated HeLa or U937 cells. High level gene expression of these TAR mutant constructs in phorbol ester-treated Jurkat cells was eliminated by second site mutations in the enhancer region or by disruption of the tat gene.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:TAR independent activation of the human immunodeficiency virus in phorbol ester stimulated T lymphocytes. 212 73

Tat protein of human immunodeficiency virus 1 is a potent trans-activator of viral gene expression. We show that purified Tat protein stimulates transcription from viral promoters greater than 10-fold in vitro. A Tat protein mutant that does not trans-activate in vivo did not stimulate transcription in vitro. Tat trans-activation required a functional TAR RNA sequence; trans-activation was competed by the addition of in vitro synthesized wild-type TAR RNA but not by mutant TAR RNAs. That Tat protein directly interacts with the TAR RNA during trans-activation in vitro was suggested by competition with Tat peptides. Preliminary evidence suggests the involvement of a cellular factor in recognition of TAR RNA during Tat trans-activation. Analysis of Tat trans-activation in vitro will provide new mechanistic insights into this process and allow a more detailed study of the relationship between Tat protein structure and function.
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PMID:HIV-1 Tat protein trans-activates transcription in vitro. 222 77

The Tat protein of human immunodeficiency virus type 1 (HIV-1) trans-activates viral gene expression and is obligatory for virus replication. Tat function is mediated through a sequence termed TAR that comprises part of the 5'-noncoding region of all HIV-1 mRNAs. This region forms a stable stem-loop structure in vitro. Recent evidence indicates that Tat binds directly to the TAR RNA sequence, and this binding is independent of the nucleotide sequence in the loop but dependent on the integrity of the upper stem. We used the electrophoretic mobility-shift assay to identify the sequence and structure specificity of this interaction and its correlation with Tat trans-activation. We show that a 3-nucleotide bulge structure (positions +23 to +25) in TAR RNA is important for both Tat interaction with TAR RNA and Tat-mediated trans-activation of gene expression. Single base substitutions at position +23 that impair Tat-mediated trans-activation in vivo also reduce binding of Tat to TAR in vitro, suggesting that the first uridine residue in the bulge is the critical base for both functions. In contrast, mutations in the loop (positions +31 to +34) and the stem (positions +9 to +12 and +49 to +52), which reduce Tat-mediated trans-activation, had no effect on Tat binding. We also show that a Tat peptide that includes the basic region required for nucleolar localization binds to TAR RNA with the same specificity as the full-length protein. We conclude that Tat binding to TAR is necessary but not sufficient by itself to account for trans-activation.
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PMID:A bulge structure in HIV-1 TAR RNA is required for Tat binding and Tat-mediated trans-activation. 222 14

The mechanism of trans-acting regulation of transcription from the long terminal repeat (LTR) of human immunodeficiency virus (HIV) has been investigated. The roles of the cis-acting elements within HIV LTR, as well as the trans-acting factors present in HIV-infected cells, have been evaluated by an in vitro transcription system. Our observations indicate that both the sequence downstream from the CAP site of HIV LTR (located at nucleotide positions +1 to +56; called the TAR element) and the GC boxes (-77 to -45) are required for full transcriptional stimulation and that both the virus-encoded tat protein and one or more cellular factors might be involved. These results demonstrate the presence of a combinatorial regulation of HIV transcription by multiple factors, which may confer the provirus with greater flexibility in regulated viral gene expression.
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PMID:Transcriptional activation from the long-terminal repeat of human immunodeficiency virus in vitro. 237 70

The human and simian immunodeficiency viruses encode at least six gene products that apparently serve regulatory functions. To evaluate the regulation of simian immunodeficiency virus gene expression at the level of RNA splicing, we used the polymerase chain reaction to amplify and clone cDNAs corresponding to a large array of mRNAs from infected cells. We identified mRNAs that used splice acceptor sites upstream of the initiator codons for tat, rev, vpr, nef, vif, and vpx, suggesting that these proteins may be expressed from different mRNAs. We also provide hybridization data suggesting that the same splice acceptor site may be used for both rev and env mRNAs. Furthermore, we isolated both tat and rev cDNAs that utilized three alternative splice acceptor sites at the start of coding exon 2, indicating that different versions of these proteins may be encoded. Finally, approximately 10 to 20% of simian immunodeficiency virus mRNAs spliced an intron from their untranslated 5' ends, and sequences contained within this intron constituted a portion of the tat-responsive TAR element. Thus, alternative pre-mRNA splicing adds a level of complexity to simian immunodeficiency virus expression, which may affect several levels of gene regulation.
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PMID:Simian immunodeficiency virus displays complex patterns of RNA splicing. 238 18

The processes of transcription and posttranscription are assumed to proceed in close association with the nuclear matrix. In this study we demonstrated that Tat, the trans-activating protein from human immunodeficiency virus type 1 (HIV-1), binds both to the TAR region of the nascent HIV mRNAs and the nuclear matrix with high affinity. Both North/Western blotting experiments and nitrocellulose binding studies revealed that Tat binds with an association constant (K alpha) of approximately 1 x 10(9) M-1 to the TAR segment of HIV RNA; binding of Tat to this sequence which is present between position 32 and 82 downstream from the TATA box was also confirmed by gel retardation assays. Binding of Tat to TAR only occurs if the loop segment in the proposed stem-loop secondary structure of HIV leader mRNA is present. Likewise, Tat binds to the nuclear matrix with a K alpha of 7.5 x 10(7) M-1. The number of binding sites has been estimated to be 2 x 10(8)/micrograms of matrix protein, corresponding to 4 x 10(3) sites/nucleus. Tat displays its bimodal function only in the presence of Zn2+ ions. In vitro transcription experiments, using HIV-1 infected nuclei, demonstrate that beyond the TAR-region HIV RNA synthesis occurs only in the presence of Tat. Present studies indicate that Tat may function as a linker by binding of nascent HIV RNAs to the nuclear matrix.
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PMID:Functional characterization of Tat protein from human immunodeficiency virus. Evidence that Tat links viral RNAs to nuclear matrix. 240 62

Expression of the human immunodeficiency virus type 1 (HIV-1) genome is greatly dependent on the viral trans-activator protein Tat. Tat functions through the TAR element, which is represented in both viral DNA and RNA. At present, there is no definitive evidence that determines whether Tat acts through a DNA or RNA form of TAR. We have used an intramolecular mutagenesis approach to change selectively the RNA secondary structure of TAR without affecting its primary sequence. We show that a specific RNA secondary structure for TAR is needed for biological activity. Furthermore, transcripts that only transiently form a native TAR RNA hairpin, which is not maintained in the mature mRNA, are completely trans-activated by Tat, suggesting that TAR is recognized as a nascent RNA.
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PMID:Tat trans-activates the human immunodeficiency virus through a nascent RNA target. 247 93


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