Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0021051 (immunodeficiency)
 71,517 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The untranslated leader sequences of rhesus macaque simian immunodeficiency virus mRNAs form a stable secondary structure, TAR. This structure can be modified by RNA splicing. In this study, the role of TAR splicing in virus replication was investigated. The proportion of viral RNAs containing a spliced TAR structure is high early after infection and decreases at later times. Moreover, proviruses containing mutations which prevent TAR splicing are significantly delayed in replication. These mutant viruses require approximately 20 days to achieve half-maximal virus production, in contrast to wild-type viruses, which require approximately 8 days. We attribute this delay to the inefficient translation of unspliced-TAR-containing mRNAs. The molecular basis for this translational effect was examined in in vitro assays. We found that spliced-TAR-containing mRNAs were translated up to 8.5 times more efficiently than were similar mRNAs containing an unspliced TAR leader. Furthermore, these spliced-TAR-containing mRNAs were more efficiently associated with ribosomes. We postulate that the level of TAR splicing provides a balance for the optimal expression of both viral proteins and genomic RNA and therefore ultimately controls the production of infectious virions.
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PMID:Role of TAR RNA splicing in translational regulation of simian immunodeficiency virus from rhesus macaques. 162 57

The enhancer of the human neurotropic papovavirus JC virus (JCV) restricts viral transcription to glial cells. We utilized the tissue specificity of the JCV enhancer as a tool to investigate the function of human immunodeficiency virus (HIV) Tat in transcriptional activation. The reporter plasmid pJCTAR-CAT was constructed by inserting the HIV type 1 Tat-responsive element, TAR, between the JCV promoter and the chloramphenicol acetyltransferase (CAT) gene. Cotransfection of pJCTAR-CAT and pSV-Tat, an expression vector for Tat, resulted in a 50-fold increase in JCV promoter activity in cells nonpermissive for JCV expression. Both the 98-bp JCV enhancer and the HIV TAR sequences were required for transactivation of pJCTAR-CAT in nonpermissive cells. The transactivation by Tat occurred at the level of transcription, as the increase in CAT activity paralleled an increase in the steady-state levels of CAT mRNA in S1 nuclease and nuclear run-on analyses. In the presence of Tat, the JCV enhancer is functional in cells normally nonpermissive for JCV expression; therefore, our results provide unique evidence that HIV type 1 Tat may regulate the activity of specific transcription factors.
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PMID:Human immunodeficiency virus Tat transactivation: induction of a tissue-specific enhancer in a nonpermissive cell line. 165 61

A number of eucaryotic viruses have devised strategies to minimize the deleterious effects on protein synthesis caused by activation of the interferon-induced, double-stranded-RNA-activated protein kinase, P68. In a recent report, we described the down regulation of the P68 protein kinase in cells infected by human immunodeficiency virus type 1 (HIV-1) (S. Roy, M. G. Katze, N. T. Parkin, I. Edery, A. G. Hovanessian, and N. Sonenberg, Science 247:1216-1219, (1990). We now present evidence that such a decrease in amounts of P68 could be essential for HIV-1 replication because of the presence of the Tat-responsive sequence (TAR sequence) present in the 5' untranslated region of HIV-1 mRNAs, which activates the P68 kinase. We found that poly(A)+ mRNAs prepared from HIV-1-infected cells efficiently activated the protein kinase as did mRNAs from stably transformed cell lines constitutively expressing the TAR region. Furthermore, we found that TAR-containing RNAs complexed with purified P68 protein kinase in vitro by two independent assays and could be cross-linked to P68 kinase present in a HeLa cell extract. Experiments using in vitro-synthesized wild-type and mutant TAR RNAs revealed that both the efficient binding to and the activation of P68 kinase were dependent on the TAR RNA stem structure. The TAR-P68 complex could be competed out by a synthetic RNA that bound to and activated the protein kinase but not by a synthetic RNA that bound with low affinity and did not activate P68. The possible biological consequences of a P68-TAR interaction that may include the switch from latent to active virus replication are discussed.
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PMID:The integrity of the stem structure of human immunodeficiency virus type 1 Tat-responsive sequence of RNA is required for interaction with the interferon-induced 68,000-Mr protein kinase. 170 40

We have analyzed the contributory role of the human immunodeficiency virus type 1 (HIV-1) promoter and enhancers in basal and Tat-induced transcription. We found that a minimal promoter competent for basal expression is contained within sequences spanning nucleotides -43 to +80. Basal expression from this HIV-1 promoter was boosted more by the additional presence of the NF-kappa B elements than by the Sp1 elements. The minimal long terminal repeat promoter (-43 to +80), while having an intact TAR sequence, was not Tat inducible. However, the simple addition of short synthetic enhancer motifs (AP1, Oct, Sp1, and NF-kappa B) conferred Tat responsiveness. This ability to respond to Tat was in part dependent on the presence of the HIV-1 promoter. Changing the HIV-1 TATA to other eucaryotic TATA or non-TATA initiators minimally affected basal expression but altered Tat inducibility. Our findings suggest a specific context of functional promoter and enhancer elements that is optimal for Tat trans activation of the HIV-1 long terminal repeat. Our results do not allow conclusions about whether Tat acts at the level of initiation or at the level of elongation to be drawn.
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PMID:Functional roles for the TATA promoter and enhancers in basal and Tat-induced expression of the human immunodeficiency virus type 1 long terminal repeat. 172 76

A comparative analysis of TAR RNA structures in human and simian immunodeficiency viruses reveals the conservation of certain structural features despite the divergence in sequence. Both the TAR elements of HIV-1 and SIV-chimpanzee can be folded into relatively simple one-stem hairpin structures. Chemical and RNAase probes were used to analyze the more complex structure of HIV-2 TAR RNA, which folds into a branched hairpin structure. A surprisingly similar RNA conformation can be proposed for SIV-mandrill, despite considerable divergence in nucleotide sequence. A third structural presentation of TAR sequences is seen for SIV-african green monkey. These results are generally consistent with the classification of HIV-SIV viruses in four subgroups based on sequence analyses (both nucleotide- and amino acid-sequences). However, some conserved TAR structures were detected for members of different virus subgroups. It is therefore proposed that RNA structure analysis might provide an additional tool for determining phylogenetic relationships among the HIV-SIV viruses.
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PMID:Structural features in TAR RNA of human and simian immunodeficiency viruses: a phylogenetic analysis. 173 99

The human immunodeficiency virus-1 (HIV-1) trans-activator Tat is an attractive target for the development of antiviral drugs because inhibition of Tat would arrest the virus at an early stage. The drug Ro 5-3335 [7-chloro-5-(2-pyrryl)-3H-1,4-benzodiazepine-2(H)-one], inhibited gene expression by HIV-1 at the level of transcriptional trans-activation by Tat. The compound did not inhibit the basal activity of the promoter. Both Tat and its target sequence TAR were required for the observed inhibitory activity. Ro 5-3335 reduced the amount of cell-associated viral RNA and antigen in acutely, as well as in chronically infected cells in vitro (median inhibition concentration 0.1 to 1 micromolar). Effective inhibition of viral replication was also observed 24 hours after cells were transfected with infectious recombinant HIV-1 DNA. The compound was active against both HIV-1 and HIV-2 and against 3'-azido-3'-deoxythymidine (AZT)-resistant clinical isolates.
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PMID:Inhibition of HIV replication in acute and chronic infections in vitro by a Tat antagonist. 176 31

The human immunodeficiency virus type 1 Tat protein binds to an RNA stem-loop structure called TAR which is present at the 5' end of all human immunodeficiency virus type 1 transcripts. This binding is centered on a bulge within the stem of TAR and is an essential step in the trans-activation process which results in a dramatic increase in viral gene expression. By analysis of a series of TAR derivatives produced by transcription or direct chemical synthesis, we determined the structural and chemical requirements for Tat binding. Tat binds well to structures which have a bulge of two to at least five unpaired bases bounded on both sides by a double-stranded RNA stem. This apparent flexibility in bulge size is in contrast to an absolute requirement for an unpaired uridine (U) in the 5'-most position of the bulge (+23). Substitution of the U with either natural bases or chemical analogs demonstrated that the imido group at the N-3 position and, possibly, the carbonyl group at the C-4 position of U are critical for Tat binding. Cytosine (C), which differs from U at only these positions, is not an acceptable substitute. Furthermore, methylation at N-3 abolishes binding. While methylation of U at the C-5 position has little effect on binding, fluorination reduces it, possibly because of its effects on relative tautomer stability at the N-3 and C-4 positions. Thus, we have identified key moieties in the U residue that are of importance for the binding of Tat to TAR RNA. We hypothesize that the invariant U is involved in hydrogen bond interactions with either another part of TAR or the TAR-binding domain in Tat.
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PMID:Critical chemical features in trans-acting-responsive RNA are required for interaction with human immunodeficiency virus type 1 Tat protein. 189 80

Toward gene therapy for the treatment of human immunodeficiency virus type 1 (HIV-1) infections in AIDS, Moloney murine leukemia virus-derived retroviral vectors were engineered to allow constitutive and tat-inducible expression of an HIV-1 5' leader sequence-specific ribozyme (Rz1). These vectors were used to infect the human CD4+ lymphocyte-derived MT4 cell line. The stable MT4 transformants expressing an HIV-1 RNA-specific ribozyme, under the control of the herpes simplex virus thymidine kinase (tk) promoter, were found to be somewhat resistant to HIV-1 infection as virus production was delayed. In cells allowing ribozyme expression under control of the simian virus 40 or cytomegalovirus promoter, the rate of HIV-1 multiplication was slightly decreased, and virus production was delayed by about 14 days. The highest level of resistance to HIV-1 infection was observed in MT4 cells transformed with a vector containing a fusion tk-TAR (trans activation-responsive) promoter to allow ribozyme expression in a constitutive and tat-inducible manner; no HIV-1 production was observed 22 days after infection of these cells. These results indicate that retroviral vectors expressing HIV-1 RNA-specific ribozymes can be used to confer resistance to HIV-1 infection.
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PMID:Resistance to human immunodeficiency virus type 1 (HIV-1) infection in human CD4+ lymphocyte-derived cell lines conferred by using retroviral vectors expressing an HIV-1 RNA-specific ribozyme. 189 2

Replication of human immunodeficiency virus requires binding of the viral Tat protein to its RNA target sequence TAR; peptides derived from Tat bind to a TAR "contact site" spanning 5 bp and a trinucleotide pyrimidine bulge. We find that high affinity binding requires a U residue in the bulge loop and 2 specific adjacent base pairs. Other bulged RNAs bind in a lower affinity nonspecific manner; sequence-specific binding requires a bulge loop of more than 1 nucleotide. Reaction with diethyl pyrocarbonate indicates that one effect of the bulge is to make the otherwise deep and narrow RNA major groove accessible. A model consistent with these data involves local distortion of A-form geometry at the bulge, which bends the helix and permits protein binding and interactive access in the RNA major groove.
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PMID:RNA recognition by Tat-derived peptides: interaction in the major groove? 190 91

The Tat protein coded by human immunodeficiency virus (HIV) is a strong activator of viral gene expression from the long terminal repeat (LTR). It appears that Tat-mediated trans-activation of the HIV LTR is predominantly a transcriptional event. It has been reported that Tat acts at the level of both transcriptional initiation and elongation through interaction with a nascent RNA target sequence termed TAR (for trans-activation response element). However, the precise mechanism(s) by which Tat mediates TAR-dependent transcriptional activity is not known. To determine whether Tat functions similarly to other eukaryotic transcriptional activators through any of the conventional promoter elements, we tested Tat activity on synthetic promoters containing consensus sequences required for binding transcription factor Sp1 and a TATA box. Here, we report that a chimeric Tat protein targeted to the promoter region by the DNA-binding domain of yeast transcription factor GAL4 activates the synthetic promoter. Because this trans-activation depends on Sp1-binding sites, Tat can apparently mediate transcriptional activation through its interaction with Sp1. Mutational analysis of the gal4-tat chimeric gene reveals that the N-terminal 48-amino acid region of Tat constitutes the activation region for Sp1-dependent trans-activation. This region of Tat exhibits substantially more activity than the N-terminal 58 amino acids of Tat, which includes the arginine-rich basic region. Effects of specific mutations in the 48-amino acid Tat region of GAL4-Tat on trans-activation of the synthetic promoter mimic the effects of these specific mutations on Tat-mediated trans-activation of the HIV-1 LTR, suggesting that trans-activation of both the synthetic promoter and the intact LTR occurs by a common mechanism.
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PMID:Sp1-dependent activation of a synthetic promoter by human immunodeficiency virus type 1 Tat protein. 192 10


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