Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

cis-acting inhibitory region (IR) sequences were identified within the gag/pol gene of the human immunodeficiency virus type 1 (HIV-1) by using a novel feedback-stimulated, rev-independent tat reporter gene to screen HIV-1 sequences in transient expression assays. Two regions, a 1,295-nucleotide segment in the gag gene (IR-1) and a 1,932-nucleotide segment of the pol gene (IR-2), each inhibited reporter gene expression 10- to 20-fold. IR-1 and IR-2 both contained subsequences which inhibited reporter gene expression. Introduction of IR sequences into a heterologous reporter plasmid, pCMV-CAT, resulted in decreased chloramphenicol acetyltransferase expression, suggesting that the inhibitory effect was not restricted to a reporter gene under the control of the HIV-1 promoter. The presence of HIV IR sequences in cis did not alter relative levels of reporter gene RNA; however, fractionation studies revealed IR-containing RNA accumulated in the nucleus. These findings demonstrate that IR sequences within the gag/pol region affect gene expression by altering the cellular distribution of viral RNA.
...
PMID:Identification of posttranscriptionally active inhibitory sequences in human immunodeficiency virus type 1 RNA: novel level of gene regulation. 165 66

We have been studying the role of human cytomegalovirus (HCMV) as a potential cofactor in human immunodeficiency virus (HIV)-related disease. The clinical relevance of HCMV is highlighted by the fact that it is a principal viral pathogen in patients with AIDS and is known to infect the same cells as HIV. In this study, we focused on the molecular interactions between HIV and HCMV in human fibroblasts and in the human glioblastoma/astrocytoma-derived cell line U373 MG, cells which can be productively infected by both viruses. Because these cells are CD4-, we used HIV pseudotyped with a murine amphotropic retrovirus as described previously (D. H. Spector, E. Wade, D. A. Wright, V. Koval, C. Clark, D. Jaquish, and S. A. Spector, J. Virol. 64:2298-2308, 1990). Initial studies showed that when cells were preinfected with HIV (Ampho-1B) for 5 days and then superinfected with HCMV, HIV antigen production dropped significantly in the coinfected cells but continued to rise in cells infected with HIV (Ampho-1B) alone. HCMV production, however, was unaffected by the presence of HIV. Further analysis showed that HIV steady-state RNA levels and gag and env protein production were also inhibited in the presence of HCMV. The transcriptional inhibition of HIV was particularly surprising in view of the previous results of several other laboratories as well as our own that HCMV infection stimulates HIV long terminal repeat-chloramphenicol acetyltransferase (LTR-CAT) expression in transient expression assays. To investigate this further, we transfected the HIV LTR-CAT construct into either uninfected cells or cells which had been preinfected with HIV. The cells were infected with HCMV 24 h posttransfection and assayed for CAT gene expression at 48 h after HCMV infection. Although there was some stimulation of the LTR-CAT in cells that were dually infected by HIV and HCMV, it was 16-fold less than that in the cells infected only with HCMV. This suggests that in the presence of the HIV infection, the stimulation of the HIV LTR-CAT gene by HCMV is significantly reduced. Experiments with UV-irradiated HCMV and the HCMV DNA polymerase inhibitor ganciclovir showed that HCMV transcription is necessary for the reduction in HIV production to occur; however, replication of the HCMV genome or any events which take place after DNA replication are not necessary. These results, coupled with the observation that inhibition is usually first seen between 8 and 24 h after HCMV infection, suggest that an HCMV early protein is involved in repression of HIV.
...
PMID:Human cytomegalovirus inhibits human immunodeficiency virus replication in cells productively infected by both viruses. 165 86

Examination of the life cycle of the human immunodeficiency virus (HIV) has shown that multiple levels of regulation exist, including some which require the virus-encoded Rev protein. In the absence of Rev, mRNAs encoding the structural proteins remain untranslated, a phenomenon which appears, in part, to be caused by nuclear entrapment of these RNA species. To examine the basis for repression of structural gene mRNA expression, a heterologous assay system was utilized to determine whether regions present within gag and pol contain elements capable of suppressing gene expression when present in cis. Both genes were found to contain cis-acting repressor sequences (CRS) that block gene expression when present within the 3' untranslated portion of a heterologous gene transcript. The element within pol was found to have the strongest repressive effect. While Rev alone was unable to reverse the repression observed with the pol sequence, addition of the env Rev-responsive element (RRE) in cis and Rev in trans did cause reversal of inhibition. Deletion mutagenesis defined a 260-bp element within the 3' portion of pol that contains a potent CRS which functions when present in the sense orientation. The corresponding region in HIV-2 pol was found to contain a functionally similar CRS element. To examine the mechanism of repression, the effects of the CRS elements on both the abundance and subcellular distribution of the mRNAs were examined. Neither was dramatically altered when examined in the context of a heterologous reporter (chloramphenicol acetyltransferase) mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Identification and characterization of intragenic sequences which repress human immunodeficiency virus structural gene expression. 189 85

The complete nucleotide sequence of one representative rat genomic unit flanked on both sides with RAL elements, which have structural features specific to retroviral LTRs (1), was determined. The total unit was about 7.5 kbp long, and there was a partial homology to known retroviral sequences in gag, pol, and env regions. The sequence also contained minus- and plus-strand primer binding sites, thereby indicating a retroviral nature in replication. Transcription of the sequence was extensive in tumor cells and was strongly correlated with the state of methylation within 5' LTRs, which were highly methylated in the normal but not in the tumor state. In functional assays with bacterial chloramphenicol acetyltransferase constructs containing a series of deleted LTRs, there seemed to be both positive and negative cis-acting effector sequences.
...
PMID:Isolation and characterization of a family of rat endogenous retroviral sequences. 281 96

A cis-acting regulatory element within the gag gene of avian retroviruses has been localized by deletion analysis, and sites of protein interaction have been studied by DNase I footprinting. Unidirectional deletions were made from both the 5' and 3' ends of a 656-base-pair fragment of the gag gene of Fujinami sarcoma virus. These deletion mutants were tested for enhancer activity in a chloramphenicol acetyltransferase transient expression assay. A sharp 5' boundary for enhancer activity was observed between 776 and 786 nucleotides downstream from the transcription initiation site. In contrast, deletion from the 3' side resulted in a gradual loss of enhancer activity, reaching a near basal level of activity by nucleotide 868. Internal deletion of 76 nucleotides just downstream of the 5' boundary abolished enhancement. Mutagenesis of a consensus enhancer core sequence (GTGGTTTG) showed that this sequence was not necessary for enhancer activity in our transient assays. DNase I footprinting with both a highly purified enhancer-binding protein from rat liver (EBP20) and a partially purified chicken liver nuclear extract showed specific protection of nucleotides 813 to 872 within the localized enhancer region. Footprinting of unidirectional deletion mutants that had lost activity indicated that this binding was not sufficient to confer enhancement.
...
PMID:Localization and footprinting of an enhancer within the avian sarcoma virus gag gene. 283 11

We isolated the full length provirus of human T cell leukaemia virus type I (HTLV-I) from MT-2, a lymphoid cell line producing HTLV-I. In three non-lymphoid cell lines (COS7, human osteosarcoma HOS cells, and HeLa) this provirus expressed a trans-acting activity after co-transfection with a recombinant plasmid carrying a bacterial chloramphenicol acetyltransferase gene under the control of a long terminal repeat of HTLV-I provirus. The trans-acting protein p40 was detected by immunoprecipitation in transfected HOS cells. Structural proteins of HTLV-I, the gag and env products, were also formed and processed in the same manner as observed in MT-2 cells. In transfected HeLa cells, the p40 protein was mainly localized in the nucleus, while other structural proteins were detected in the cytoplasm and/or the membrane by indirect immunofluorescence. Syncytium formation was observed in HeLa cells after transfection. These results demonstrated that non-lymphoid cells could produce the major proteins of HTLV-I after DNA transfection of the cloned provirus.
...
PMID:Expression of a provirus of human T cell leukaemia virus type I by DNA transfection. 302 87

A cis-acting enhancer element has been detected within the gag gene of several avian retroviruses, including Rous sarcoma virus, Fujinami sarcoma virus, and the endogenous Rous-associated virus-0. A consensus enhancer core sequence, GTGGTTTG, is present in all of these viral genomes, approximately 900 bases downstream from the site of initiation of transcription. When an internal fragment derived from the gag gene of any of these viruses (spanning nucleotides 533 to approximately 1149) was inserted into a plasmid containing the chloramphenicol acetyltransferase (cat) gene under control of the simian virus 40 promoter, 9- or 21-fold enhancement of CAT expression was observed after transfection into mouse L cells and chicken embryo fibroblasts, respectively. This enhancement was not dependent on the position of insertion of the gag fragment into the plasmid. However, there was a strong dependence on orientation, with higher levels of CAT expression in constructs in which the 5' end of the gag fragment was nearest to the promoter, suggesting a possible negative regulatory element at the 3' end of this fragment. Deletion of the 3' end of the insert resulted in a gag fragment, containing nucleotides 533 to 1017, which enhanced expression equally in either orientation. When the gag fragment was inserted into a plasmid containing the cat gene under the control of an intact Rous sarcoma virus long terminal repeat, it induced a two- to threefold increase in CAT activity and CAT mRNA levels. Translation of the gag fragment did not appear to be necessary for the observed enhancement, since two insertional mutations resulting in frameshifts in the gag insert did not affect CAT expression. However, deletion of a 330-base internal fragment from the gag insert restored a basal level of CAT activity. These results suggest that retroviruses have regulatory elements within their genes distinct from those in the long terminal repeats that flank the genes.
...
PMID:cis-acting regulatory elements within gag genes of avian retroviruses. 303 70

ML, a transplantable T-cell leukemia of DBA/2 mice, expresses the gag and env gene products of the murine mammary tumor virus (MuMTV). Analysis of the genomic DNA of ML cells using the restriction enzyme HindIII and hybridization with MuMTV-specific probes revealed that the ML cells contained two or more newly integrated MuMTV proviruses (ML-MuMTV). Further analysis of these proviruses with a combination of Mspl and Pstl enzymes showed that the long terminal repeat (LTR) (ML-MuMTV LTR) of the ML-MuMTV provirus(es) was structurally different from the LTRs of both exogenous and endogenous MuMTV proviruses of DBA/2 mice. In order to characterize the nature of the structural alterations in the ML-MuMTV LTR, we cloned a 4.0-kb HindIII fragment containing the 3' half of an acquired provirus. Sequence analysis of the ML-MuMTV LTR of this acquired provirus revealed a deletion of a 387-bp segment that maps between the 5' nucleotide 616 and the 3' nucleotide 1003 of the normal MuMTV LTR and duplication of a 102-bp fragment that mapped between 514 and 616. In addition to two point mutations in the direct repeat, the proviral ML-MuMTV LTR has also acquired 9- and 7-bp segments at the 5' and 3' sites of the duplicated 102-bp segment, respectively. Since direct repeats in the U3 regions of a number of LTRs have been found to be associated with enhancer function, we examined the enhancer function of the U3 region sequences of the ML-MuMTV LTR using enhancer-dependent transient expression assay of chloramphenicol acetyltransferase (CAT) gene in NIH 3T3 cells. Our studies have shown that the U3 region sequences of the rearranged ML-MuMTV LTR have the ability to enhance the expression of the CAT gene 12- to 15-fold more than the U3 region sequences from the normal MuMTV LTR. The presence of a direct repeat in the ML-MuMTV LTR and its ability to enhance the transcription of adjacent genes is analogous to the LTRs of certain murine leukemia viruses.
...
PMID:Structural alterations in the long terminal repeat of an acquired mouse mammary tumor virus provirus in a T-cell leukemia of DBA/2 mice. 303 82

Previously we demonstrated an inhibitory effect of interleukin-4 (IL-4) on establishment of human immunodeficiency virus type 1 (HIV-1) infection in primary macrophages. The reported similarities between the biological effects of IL-4 and IL-10 prompted us to study the effect of IL-10 on HIV-1 replication. Treatment of primary macrophages with IL-10 resulted in inhibition of HIV-1 infection. This inhibitory effect was specific for macrophages, since IL-10 did not interfere with HIV-1 replication in primary T cells. Semiquantitative PCR analysis excluded an inhibitory effect of IL-10 on virus entry and reverse transcription. Effects of IL-10 on HIV-1 long terminal repeat-driven chloramphenicol acetyltransferase activity also could not be demonstrated in a transient expression system in primary derived macrophages. In agreement with this, Northern (RNA) blot analysis demonstrated equal amounts of viral RNA species irrespective of IL-10 treatment, also excluding an inhibitory effect on elongation of virus transcription. Monocyte-derived macrophages (MDM) treated with IL-10 after HIV-1 inoculation showed accumulation of apparently mature p24 protein suggestive of an inhibitory effect at the level of virus assembly. IL-10 treatment of MDM prior to HIV-1 inoculation did not result in accumulation of p24 protein. Immunoblot analysis indeed showed the absence of mature p24 and gp120 but accumulation of the Pr53 gag-encoded protein in HIV-1-inoculated, IL-10-pretreated MDM, suggesting an inhibitory effect at the level of protein processing. A combination of IL-4 and IL-10 resulted in a cumulative inhibitory effect on HIV-1 replication in MDM. The recent observation that in the course of HIV-1 infection a shift occurs in the production of IL-2/gamma interferon toward enhanced IL-4 and IL-10 production and the reported shift from preferential macrophage-tropic towards preferential T-cell-tropic HIV-1 variants with progression of disease suggest that cytokines have an important role in the in vivo regulation of HIV-1 tropism.
...
PMID:Interference of interleukin-10 with human immunodeficiency virus type 1 replication in primary monocyte-derived macrophages. 793 78

We have previously described replication-competent Schmidt Ruppin-A Rous sarcoma virus (RSV)-based retroviral vectors that can be used to deliver and express genes in avian cells. We have continued to modify the prototype vectors to develop a more versatile and efficient system. Substitution of the polymerase (pol) region from the Bryan high-titer RSV (BH-RSV) for the SR-A RSV pol region of these retroviral vectors causes these viruses to replicate more efficiently. We cloned the gag regions from two independent BH-RSV-transformed cell lines and tested whether substituting either of these gag regions would improve the replication and/or gene expression of the vectors. Chimeric vectors were constructed in which the gag region of the prototype vector (SR-A RSV) was replaced with the corresponding segment of BH-RSV gag in vectors that had either the original SR-A RSV pol or the BH-RSV pol region. All vectors contained the bacterial chloramphenicol acetyltransferase gene (CAT). The results indicate that different SR-A RSV and BH-RSV gag-pol chimeras can significantly affect the level of viral and CAT gene expression. The insertion of one of the BH-RSV gag regions, but not the other, gave rise to viruses with unstable genomes.
...
PMID:Effects of the gag region on genome stability: avian retroviral vectors that contain sequences from the Bryan strain of Rous sarcoma virus. 805 45


1 2 Next >>

---