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PubMed1990

Transactivation of the Rous sarcoma virus long terminal repeat promoter by Marek's disease virus.

Transient expression of chloramphenicol acetyltransferase (CAT) was used to study Marek's diseases virus (MDV)-mediated transactivation of the Rous sarcoma virus long terminal repeat (RSV-LTR) promoter. Cotransfection experiments in primary avian cells were conducted using MDV high-molecular-weight DNA and plasmid pRSVcat. Increased CAT activity, relative to controls, was consistently observed in the presence of MDV. Enhanced CAT activity, expressed via the RSV-LTR promoter, was strictly dependent on the presence of MDV DNA or virus, suggesting that activation of the RSV-LTR promoter was due to factors expressed in MDV-infected cells. Differences in transactivation efficiency were observed between various strains and the serotypes of MDV. In particular, high- and low-passage pairs of serotype 1 MDV showed marked differences in their ability to increase CAT activity in pRSVcat-transfected cells. Attenuation of viral pathogenicity and decreased expression of some cell surface glycoproteins occur in high-passage MDV strains. Decreased transactivation ability in these same strains suggests that continuous passage in culture and attenuation may perturb a regulatory mechanism operating by transcriptional control. In addition, transactivation of the RSV-LTR promoter suggests that increased incidence of avian leukosis following vaccination by MDV may be due to MDV-mediated transactivation of endogenous ALV proviral LTR promoters. MDV-mediated transactivation was not limited to the RSV-LTR promoter. Serotype 3 MDV (HVT) efficiently transactivated the herpes simplex virus (HSV) alpha 4 (ICP4) and beta-TK promoters as well as the human cytomegalovirus (hCMV) immediate early promoter.

Animals↗
PubMed1992

Amphotropic retroviruses with a hybrid long terminal repeat as a tool for gene therapy of cystic fibrosis.

We have made two retroviral vectors encoding the bacterial beta-galactosidase (lacZ) as a marker gene and a long terminal repeat (LTR) containing an enhancer of the polyoma F101 virus [symbol: see text]. One vector, [symbol: see text], can be used as a test vector in grafting, lineage analysis and gene therapy studies. The other, [symbol: see text] carries an additional unique cloning site in which a gene of interest can be cloned. Titration experiments showed that in human epithelial cell lines, [symbol: see text] produces a transcriptionally active integration more often than the commonly used BAG vector with the wild type LTR. Human epithelial cells in primary culture could be successfully infected. Our data suggest that gene therapy protocols requiring infection in situ, such as in the case of cystic fibrosis, will be hampered by the relatively low local titres that can be achieved at present.

Cell Line↗
PubMed1982

Carcinogen- and radiation-transformed C3H 10T1/2 cells contain RNAs homologous to the long terminal repeat sequence of a murine leukemia virus.

Carcinogen- or radiation-transformed C3H 10T1/2 murine fibroblasts transcribe a set of poly(A)+RNAs that contain sequences homologous to the long terminal repeat (LTR) sequence of Moloney murine sarcoma virus. These LTR-containing RNAs consist of a series of discrete bands ranging in size from about 38 to 18 S. The higher molecular weight molecules (30-38 S) in this set of RNAs also contain sequences homologous to the gag, pol, and env genes of a murine leukemia virus. A 24S RNA contains sequences homologous to the env gene of murine leukemia virus. A 20S and an 18S RNA also share homology with the LTR probe but fail to hybridize to the gag, pol, or env probes or to a probe for the U3 region of the LTR sequence. Thus, the latter transcripts do not appear to arise from a known endogenous murine leukemia virus genome. Although this entire set of RNAs is absent from normal C3H 10T1/2 cells (or is present at an extremely low level), these RNAs are induced by BrdUrd or 5-azacytidine. The presence of these RNAs may provide highly sensitive molecular markers of transformation of murine cells.

Animals↗
PubMed1983

A small region of the mouse mammary tumor virus long terminal repeat confers glucocorticoid hormone regulation on a linked heterologous gene.

Expression of mouse mammary tumor virus (MMTV) proviruses is transcriptionally regulated by glucocorticoid hormones. We have linked the MMTV long terminal repeat (LTR) to the coding region of the herpes simplex virus thymidine kinase gene and used this construction to characterize sequences within the LTR that are involved in glucocorticoid regulation. Our results show that 290 base pairs (bp) of the MMTV LTR, including 190 bp upstream from the start site for transcription, are sufficient to confer regulation on the downstream gene. Deletion of an additional 50 bp, leaving sequences from position -140 to +100, eliminates the response. However, the constitutive level of expression is maintained even after deletion of sequences upstream from position -80, indicating that sequences required for the hormone response can be distinguished from those required for basal expression. We also have shown, by making a 4-bp insertion or a 20-bp deletion around position -107, that the distance between the putative signal for hormone response and the start site of transcription can be varied without affecting regulation. Furthermore, replacement of MMTV sequences from position -59 to +100 with analogous sequences from the Rous sarcoma virus LTR does not change the regulation.

Animals↗
PubMed1987

Identification of p40x-responsive regulatory sequences within the human T-cell leukemia virus type I long terminal repeat.

Distinct transcriptional regulatory sequences located within the upstream sequences required for p40x trans-activation of the human T-cell leukemia virus type I (HTLV-I) long terminal repeat (LTR) were chemically synthesized and cloned upstream of the basal HTLV-I LTR promoter. Plasmids containing a single 21-base-pair (bp) repeat were weakly inducible by p40x. The level of trans-activation by p40x was increased when two (30-fold) or three (40-fold) 21-bp repeats were present in the upstream control region. In the mutant containing two 21-bp repeats, the upstream 21-bp repeat could be positioned in either the sense (30-fold) or the antisense (16-fold) orientation. Plasmids containing a 51-bp repeat element, which included a single 21-bp repeat, were induced to levels similar to that obtained with the 21-bp repeat sequence alone. Template DNAs containing a single copy of the HTLV-I sequences between -117 and -160 were stimulated approximately 10-fold by p40x when one copy of the 21-bp element was located downstream.

Base Sequence↗
PubMed1990

The Epstein-Barr virus BRLF1 immediate-early gene product transactivates the human immunodeficiency virus type 1 long terminal repeat by a mechanism which is enhancer independent.

The Epstein-Barr virus (EBV) immediate-early gene product, BRLF1, transactivates the human immunodeficiency virus type 1 (HIV-1) long terminal repeat. BRLF1-induced transactivation of HIV-1 promoter constructs is accompanied by an increase in plasmid mRNA and is reporter gene independent. Previously, BRLF1 transactivation of EBV promoters has been mapped to regions which function as enhancer elements. Deletional analysis demonstrates that BRLF1 transactivation of the HIV-1 promoter does not require the HIV-1 enhancer. Thus, the EBV BRLF1 gene product may transactivate by at least two different mechanisms, one mechanism involving certain enhancer elements and another mechanism which is enhancer independent.

Antigens, Viral↗
PubMed2004

Transcription regulatory complexes bind the human T-cell leukemia virus 5' and 3' long terminal repeats to control gene expression.

The human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus that integrates randomly into the T-cell genome. Two long terminal repeats (LTRs) flank the integrated provirus. The upstream and downstream LTRs carry identical promoter sequences. Studies with other retroviruses suggest that the downstream promoter is silent and that RNA polymerases initiating at the upstream promoter proceed through the 3' LTR. In this study, we used the chromatin immunoprecipitation assay to compare the binding of transcription regulatory proteins at both the upstream and downstream promoters in HTLV-1-infected cell lines and adult T-cell leukemia-lymphoma cells. Unexpectedly, we detected a nearly equal distribution of activator (Tax, CREB, ATF-1, ATF-2, c-Fos, and c-Jun) and regulatory protein (CBP, p300, TAF(II)250, and polymerase II) binding at both the upstream and downstream promoters. Consistent with this observation, we found that the downstream promoter was transcriptionally active, suggesting that the two promoters are functionally equivalent. We also detected asymmetrical binding of histone deacetylases (HDAC-1, -2, and -3) at both promoters. All three HDACs strongly repressed Tax transactivation, and this repression correlated with displacement of Tax from the HTLV-1 promoter. These effects were reciprocal, as Tax expression reversed HDAC repression and displaced HDACs from the HTLV-1 promoter. These data suggest that HTLV-1 transcriptional regulation at both the 5' and 3' LTRs is mediated, in part, through the mutually exclusive binding of Tax and HDACs at the proviral promoters.

3' Flanking Region↗
PubMed2005

Retrovirus-like long-terminal repeat DQ-LTR13 and genetic susceptibility to type 1 diabetes and autoimmune Addison's disease.

Controversial data are available on the association between the retrovirus-like long-terminal repeat (LTR) DQ-LTR13 and genetic susceptibility to type 1 diabetes and other autoimmune diseases. We analyzed DNA samples from 315 type 1 diabetic patients, 166 autoimmune Addison's disease (AAD) patients, 1,054 healthy subjects, and 144 families of type 1 diabetic offspring. DQ-LTR13 was more frequent among patients than healthy subjects (P(c) < 0.0006), and a preferential transmission of DQB1*0302-LTR13(+) from parents to type 1 diabetic offspring was observed. DQ-LTR13 was in linkage disequilibrium (LD) with DQB1*0302 but not DQB1*0201. The presence of DQ-LTR13 increased the odds ratio of DQB1*0302 2.9- to 3.2-fold for type 1 diabetes and AAD. DRB1*0403 was absent in all of the 169 DRB1*04-positive patients but present in 27% (34 of 127) DRB1*04-positive healthy subjects (P(c) < 0.001). DQ-LTR13 was detected in 1 of 34 (3%) DRB1*0403-positive healthy subjects and 36 of 93 (39%) individuals carrying another DRB1*04 allele (P(c) = 0.002). Multivariate logistic regression analysis revealed that DQ-LTR13 is not independently associated with type 1 diabetes and AAD after correction for DQB1*0302 and DRB1*0403. Conversely, DQB1*0201, DQB1*0302, DRB1*0401, and DRB1*0403 were all significantly associated with disease risk also after correction for DQ-LTR13. We provide conclusive evidence that the genetic association of DQ-LTR13 with type 1 diabetes and AAD is primarily due to a LD with DQB1*0302 and DRB1*0403.

Addison Disease↗
PubMed1995

Interaction of virion protein Vpr of human immunodeficiency virus type 1 with cellular transcription factor Sp1 and trans-activation of viral long terminal repeat.

Acquired immunodeficiency syndrome (AIDS) is a result of replication of the human immunodeficiency virus type 1 (HIV-1) predominantly in CD4+ T lymphocytes and macrophages. However, most of these cells in vivo are immunologically quiescent, a condition restricting HIV-1 replication. Vpr is an HIV-1 virion protein suspected to enhance HIV-1 replication in vivo. We demonstrate in this report that Vpr specifically activates HIV-1 long terminal repeat (LTR)-directed transcription. This effect is most pronounced on a minimal promoter from HIV-1 LTR containing the TATA box and binding motifs for the ubiquitous cellular transcription factor Sp1. Evidence is presented that Vpr interacts with Sp1 when Sp1 is bound to the Sp1 motifs within the HIV-1 LTR Both Vpr-Sp1 interaction and Vpr trans-activation require a central Leu/Ile-rich domain in Vpr. Our findings suggest that Vpr trans-activation through Sp1 is most critical for the immediate early transcription of HIV-1 when other positive regulators, such as NF-kappa B, are limited or inactive, a condition presumably present in vivo. By interacting with Sp1, Vpr also has the potential to influence cellular gene expression and cellular functions. Thus, therapeutic approaches directed toward blocking the Vpr trans-activation function could prove valuable in treating AIDS.

Base Sequence↗
PubMed1997

Activation of HIV-1 long terminal repeat transcription and virus replication via NF-kappaB-dependent and -independent pathways by potent phosphotyrosine phosphatase inhibitors, the peroxovanadium compounds.

Replication of human immunodeficiency virus type 1 (HIV-1) is increased by different cytokines and T cell activators, also known to modulate tyrosine phosphorylation levels. A novel class of protein tyrosine phosphatase (PTP) inhibitors, peroxovanadium (pV) compounds, were tested for a putative effect on HIV-1 long terminal repeat (LTR) activity. We found that these PTP inhibitors markedly enhanced HIV-1 LTR activity in 1G5 cells, a stably transfected cell line that harbors an HIV-1 LTR-driven luciferase construct. A direct correlation between the extent of tyrosine phosphorylation and the level of HIV-1 LTR inducibility was seen after treatment with three different pV compounds. Transient transfection experiments were carried out in several T cell lines, and after addition of pV, a marked increase in HIV-1 LTR activity was measured. Monocytoid cells were tested using U937-derived cell lines and were also found to be sensitive to the pV-mediated potentiating effect on HIV-1 LTR activity. A significant reduction of the pV-mediated increase in HIV-1 LTR activity was seen in cells transiently transfected with an HIV-1 LTR-driven luciferase construct bearing a mutation in both NF-kappaB binding sites although detectable levels of induction remained. Electrophoretic mobility shift assays allowed the identification of the nuclear translocation of the NF-kappaB p50.p65 heterodimer complex induced by pV compounds. A dominant negative version of the repressor IkappaBalpha mutated on serines 32 and 36 impeded pV-induced NF-kappaB-dependent luciferase activity. Western blot analysis showed a clear diminution in the protein level of IkappaBalpha starting 30 min after pV treatment of Jurkat E6.1 cells which is indicative of its degradation. On the other hand, no increase in tyrosine phosphorylation was observed on IkappaBalpha itself. Finally, we tested the PTP inhibitors on four cell lines latently infected with HIV-1 and showed a consistent pV-mediated increase in virion production. Thus, our studies suggest that pV-mediated activation of HIV-1 LTR activity is controlled by the nuclear translocation of the NF-kappaB transcription factor, which is mediated by IkappaBalpha serine phosphorylation and degradation, but also by a still undefined NF-kappaB-independent pathway.

Cell Line↗
PubMed1999

Characterization of the Jembrana disease virus tat gene and the cis- and trans-regulatory elements in its long terminal repeats.

Jembrana disease virus (JDV) is a newly identified bovine lentivirus that is closely related to the bovine immunodeficiency virus (BIV). JDV contains a tat gene, encoded by two exons, which has potent transactivation activity. Cotransfection of the JDV tat expression plasmid with the JDV promoter chloramphenicol acetyltransferase (CAT) construct pJDV-U3R resulted in a substantial increase in the level of CAT mRNA transcribed from the JDV long terminal repeat (LTR) and a dramatic increase in the CAT protein level. Deletion analysis of the LTR sequences showed that sequences spanning nucleotides -68 to +53, including the TATA box and the predicted first stem-loop structure of the predicted Tat response element (TAR), were required for efficient transactivation. The results, derived from site-directed mutagenesis experiments, suggested that the base pairing in the stem of the first stem-loop structure in the TAR region was important for JDV Tat-mediated transactivation; in contrast, nucleotide substitutions in the loop region of JDV TAR had less effect. For the JDV LTR, upstream sequences, from nucleotide -196 and beyond, as well as the predicted secondary structures in the R region, may have a negative effect on basal JDV promoter activity. Deletion of these regions resulted in a four- to fivefold increase in basal expression. The JDV Tat is also a potent transactivator of other animal and primate lentivirus promoters. It transactivated BIV and human immunodeficiency virus type 1 (HIV-1) LTRs to levels similar to those with their homologous Tat proteins. In contrast, HIV-1 Tat has minimal effects on JDV LTR expression, whereas BIV Tat moderately transactivated the JDV LTR. Our study suggests that JDV may use a mechanism of transactivation similar but not identical to those of other animal and primate lentiviruses.

Amino Acid Sequence↗
PubMed1985

Nucleotide sequence and structure of integrated bovine leukemia virus long terminal repeats.

Bovine leukemia virus (BLV) proviruses, harbored by the productively infected fetal lamb kidney (FLK-BLV) cell line, were cloned in bacteriophage lambda L47. The nucleotide sequence of the proviral long terminal repeats (LTR) with flanking cell and virus DNA have been determined. The BLV LTR is 531 bp in length and is bounded by the dinucleotides 5'-TG...CA-3', which are part of a 3-bp inverted repeat. The integrated provirus is flanked by 6-bp direct repeats of cellular DNA. A tRNApro primer binding site is present starting 2 bp downstream of the 5' LTR. In addition to sequencing integrated proviral DNA clones, the nucleotide sequence of a cDNA clone, representing the 3' end of genomic viral RNA, was determined; thus revealing the RNA polyadenylation site and R:U5 boundary within the LTR. Unlike most other retroviruses, a consensus polyadenylation signal, "AATAAA," is not located proximal to the BLV polyadenylation site. The RNA initiation site, defining the U3:R boundary, was located in the BLV LTR by S1 nuclease mapping. This site is approximately 25 bp downstream of an A + T-rich region which probably encompasses a Goldberg-Hogness ("TATAA") box and about 90 bp downstream of a potential "CCAAT" box. The BLV LTR possesses a U3 region of 204 bp, an unusually long R region of 241 bp, and a U5 region of 86 bp.

Base Sequence↗
PubMed1997

Analysis of interactions between huGATA-3 transcription factor and three GATA regulatory elements of HIV-1 long terminal repeat, by surface plasmon resonance.

Relative affinities of transcriptional regulatory elements for their respective factor have been essentially studied by bandshift analysis. Here we report a real-time study of factor/DNA interactions using a surface plasmon resonance approach and further characterization of recovered proteins involved in this interaction. For this purpose, human GATA-3, either recombinant or in nuclear extracts, and three natural GATA elements of the HIV-1 long terminal repeat (sites 1, 2, and 3) were chosen, in which only site 2 is a noncanonical GATA site. Direct analysis of sensorgrams, with recombinant huGATA-3, allowed the comparison of association and dissociation profiles of the three DNA regions and their ranking according to their relative affinities. This result, confirmed by competitions with each GATA site, demonstrated the higher relative affinity (at least sevenfold) of site 3. Interactions between the canonical and unique GATA site 3 and nuclear extracts were also studied in real time and provided information on its association and dissociation rates for native huGATA-3. Finally, recovered protein was identified as genuine huGATA-3 by SDS-PAGE, Western blotting, and bandshift assays.

Base Sequence↗
PubMed2006

At least 50% of human-specific HERV-K (HML-2) long terminal repeats serve in vivo as active promoters for host nonrepetitive DNA transcription.

We report the first genome-wide comparison of in vivo promoter activities of a group of human-specific endogenous retroviruses in healthy and cancerous germ line tissues. To this end, we employed a recently developed technique termed genomic repeat expression monitoring. We found that at least 50% of human-specific long terminal repeats (LTRs) possessed promoter activity, and many of them were up- or downregulated in a seminoma. Individual LTRs were expressed at markedly different levels, ranging from approximately 0.001 to approximately 3% of the housekeeping beta-actin gene transcript level. We demonstrated that the main factors affecting the LTR promoter activity were the LTR type (5'-proviral, 3' proviral, or solitary) and position with regard to genes. The averaged promoter strengths of solitary and 3'-proviral LTRs were almost identical in both tissues, whereas 5'-proviral LTRs displayed two- to fivefold higher promoter activities. The relative content of promoter-active LTRs in gene-rich regions was significantly higher than that in gene-poor loci. This content was maximal in those regions where LTRs "overlapped" readthrough transcripts. Although many promoter-active LTRs were mapped near known genes, no clear-cut correlation was observed between transcriptional activities of genes and neighboring LTRs. Our data also suggest a selective suppression of transcription for LTRs located in gene introns.

Base Sequence↗
PubMed2002

Differential regulation of HIV-1 clade-specific B, C, and E long terminal repeats by NF-kappaB and the Tat transactivator.

The major group of human immunodeficiency viruses (HIV-1) that comprise the current global pandemic have diversified during their worldwide spread and may be divided into at least 10 distinct subtypes or clades, A through J. Subtype B predominates in North America and Europe, subtype E predominates in Southeast Asia, and subtype C predominates in sub-Saharan Africa. Functional distinctions in long terminal repeat (LTR) architecture among HIV subtypes have been identified, thus raising the possibility that regulatory divergence among the subtypes of HIV-1 has occurred. In addition to the transcriptional specificity of the HIV-1 LTR, productive HIV-1 replication is also dependent upon the viral Tat protein. Therefore, we sought to investigate whether interactions between host signaling pathways and the NF-kappaB regions of different HIV-1 subtypes, together with subtype-specific interactions between Tat, TAR, and cellular proteins, modulate the efficiency of HIV-1 clade-specific gene transcription. We demonstrate that the NF-kappaB sites of subtypes B and E both bind NF-kappaB-related complexes. However, the duplicated kappaB sites of the C subtype do not compete for NF-kappaB binding. Also, clade E Tat protein possesses the highest transactivation capacity, regardless of the LTR context. Furthermore, preliminary evidence suggests that the acetylation of subtype-specific Tat proteins may correlate with their transactivation efficiency.

Amino Acid Sequence↗
PubMed2001

Negative regulation of the NFAT1 factor by CD45: implication in HIV-1 long terminal repeat activation.

HIV-1 gene regulation is greatly dependent on the presence of the -104/-81 enhancer region which is regulated by both NF-kappaB and NFAT transcription factors. We have found that a greater induction in HIV-1 long terminal repeat-driven gene expression was observed upon PMA/ionomycin (Iono) stimulation of a CD45-deficient cell line (J45.01) in comparison to the parental Jurkat cells. Unlike NF-kappaB which was not affected by the absence of CD45, NFAT showed a much greater augmentation in nuclear translocation and transcriptional activity in J45.01 cells upon PMA/Iono stimulation. PMA/Iono-induced NFAT activation, NFAT translocation and calcium influx peaked at similar time points for both Jurkat and J45.01 cell lines. The NFAT-dependent promoters from the IL-2 and TNF-alpha genes were also more potently activated by PMA/Iono in J45.01 cells. Interestingly, higher levels of intracellular calcium were consistently demonstrated in PMA/Iono-induced CD45-deficient cell lines (J45.01 and HPB45.0). Furthermore, PMA/Iono induction of calcium mobilization in both Jurkat and J45.01 cell lines was observed to be EGTA-sensitive. Mechanistic studies revealed that CD3zeta and ZAP-70 were more heavily tyrosine phosphorylated in J45.01 cells than Jurkat cells. Analysis of the HIV-1 enhancer by EMSAs demonstrated that the bound NFAT complex was present at higher levels in J45.01 nuclear extracts and that the NFAT1 member was predominant. In conclusion, our results indicate that NFAT activation by stimuli acting in a more distal fashion from the TCR-mediated signaling pathway can be down-regulated by CD45 and that this CD45-dependent regulation in turn affects HIV-1 long terminal repeat activation.

Calcium Signaling↗
PubMed1999

Design and evaluation of a human immunodeficiency virus type 1 RNA assay using nucleic acid sequence-based amplification technology able to quantify both group M and O viruses by using the long terminal repeat as target.

Currently available human immunodeficiency virus type 1 (HIV-1) RNA quantification assays can detect most viruses of the group M subtypes, but a substantial number are missed or not quantified reliably. Viruses of HIV-1 group O cannot be detected by any commercially available assay. We developed and evaluated a quantitative assay based on nucleic acid sequence-based amplification (NASBA) technology, with primers and probes located in the conserved long terminal repeat (LTR) region of the HIV-1 genome. In 68 of 72 serum samples from individuals infected with HIV-1 subtypes A to H of group M, viruses could be detected and quantified. In serum samples from two patients infected with HIV-1 group O viruses, these viruses as well could be detected and quantified. In contrast, the currently used gag-based assay underestimated the presence of subtype A viruses and could not detect subtype G and group O viruses. The discrepancy between the results of the two assays may be explained by the number of mismatches found within and among the probe and primer regions of the subtype isolates. These data indicate that LTR-based assays, including the NASBA format chosen here, are better suited to monitoring HIV-1 therapy than are gag-based assays in an era in which multiple HIV-1 subtypes and groups are spreading worldwide.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Functional differences between the long terminal repeat transcriptional promoters of human immunodeficiency virus type 1 subtypes A through G.

The current human immunodeficiency virus type 1 (HIV-1) shows an increasing number of distinct viral subtypes, as well as viruses that are recombinants of at least two subtypes. Although no biological differences have been described so far for viruses that belong to different subtypes, there is considerable sequence variation between the different HIV-1 subtypes. The HIV-1 long terminal repeat (LTR) encodes the transcriptional promoter, and the LTR of subtypes A through G was cloned and analyzed to test if there are subtype-specific differences in gene expression. Sequence analysis demonstrated a unique LTR enhancer-promoter configuration for each subtype. Transcription assays with luciferase reporter constructs showed that all subtype LTRs are functional promoters with a low basal transcriptional activity and a high activity in the presence of the viral Tat transcriptional activator protein. All subtype LTRs responded equally well to the Tat trans activator protein of subtype B. This result suggests that there are no major differences in the mechanism of Tat-mediated trans activation among the subtypes. Nevertheless, subtype-specific differences in the activity of the basal LTR promoter were measured in different cell types. Furthermore, we measured a differential response to tumor necrosis factor alpha treatment, and the induction level correlated with the number of NF-kappaB sites in the respective LTRs, which varies from one (subtype E) to three (subtype C). In general, subtype E was found to encode the most potent LTR, and we therefore inserted the core promoter elements of subtype E in the infectious molecular clone of the LAI isolate (subtype B). This recombinant LAI-E virus exhibited a profound replication advantage compared with the original LAI virus in the SupT1 T-cell line, indicating that subtle differences in LTR promoter activity can have a significant impact on viral replication kinetics. These results suggest that there may be considerable biological differences among the HIV-1 subtypes.

Base Sequence↗