Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
 5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The long terminal repeat (LTR) of a retrovirus contains sequence elements that constitute a promoter for controlling viral gene expression in infected cells. We have examined regulation of LTR-directed gene expression in feline immunodeficiency virus (FIV), a T-lymphocytopathic lentivirus associated with a fatal AIDS-like disease in domestic cats. Two independent virus isolates, designated FIV-Petaluma and FIV-PPR, have been molecularly cloned and show greater than 85% sequence homology. Both clones (termed pF34 and pPPR) produce infectious virus after transfection of permissive feline cells. Basal promoter activity of the LTRs was measured in various cell lines in transient expression assays using plasmids containing the viral LTR linked to the bacterial chloramphenicol acetyltransferase gene. Both LTRs were strong promoters in several cell lines, although in some cell lines the pF34 LTR had four- to fivefold higher basal activity than the pPPR LTR. FIV LTR mutations affecting the first AP4 site, AP1 site, ATF site, or NF-kappa B site resulted in decreased basal activity of the FIV promoter. Mutational analysis also revealed a negative regulatory element. In cotransfection experiments, both pF34 proviral DNA and pPPR proviral DNA appeared to transactivate either the pF34 LTR or the pPPR LTR; however, levels of transactivation were very low. Cotransfection of both LTRs with FIV subgenomic clones containing various viral open reading frames resulted in low level or no transactivation. The LTRs of both FIV clones responded to cell activation signals in human T-lymphoid cells (Jurkat) treated with phytohemagglutinin and phorbol-12-myristate-13-acetate. Promoter function of both FIV LTRs was also enhanced in cells treated with either forskolin, an inducer of intracellular cyclic-AMP (c-AMP), or dibutyryl c-AMP. Analysis of site-specific mutants showed that a potential AP1 site in the U3 domain of the LTR was required for T-cell activation responses mediated by protein kinase C, whereas a putative ATF site was the target for c-AMP-induced responses mediated by protein kinase A. These studies revealed that cellular transcription factors play a significant role in regulation of FIV gene expression.
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PMID:Regulation of gene expression directed by the long terminal repeat of the feline immunodeficiency virus. 131 May 54

Nuclear protein binding sites in the long terminal repeat (LTR) of feline immunodeficiency virus (FIV) were identified by the method of DNase I footprinting. Using nuclear protein extracts from a feline T lymphoma cell line, several discrete footprints were generated upstream of the transcriptional initiation site (-50 to -150). The specificity of protein binding was examined by competition with oligonucleotides representing consensus DNA binding sites for known transcription factors. Binding to AP-1 (-124) and ATF (-58) motifs was observed, with cross-competition between these sites. A strong footprint signal was also detected over a tandemly repeated C/EBP motif (-94, -86) and an adjacent weaker footprint was found to be specific for an NF1 motif (-72/-63). The effect on FIV LTR promoter activity of progressively deleting these nuclear factor binding sites was examined by linking LTR deletion mutants to the chloramphenicol acetyltransferase (CAT) gene. Deletion of the AP-1 site caused a 10- to 25-fold loss of CAT activity whereas deletion past the ATF site reduced activity virtually to background levels. The effects of deleting the C/EBP and NF1 sites were less marked and varied according to cell type. Transactivation of the LTR was assayed using constructs linked to a CAT reporter gene. The full-length FIV LTR was not significantly trans-activated. However, the expression of a deleted LTR construct lacking the AP-4/AP-1 site but retaining C/EBP and ATF sites was partially restored by co-infection with FIV or by co-transfection with an infectious molecular clone of FIV (FIV-PPR). These results show that host transcription factors responsive to cellular activation have a major role in regulating FIV expression, and suggest that virus-coded trans-activators acting through U3 may play a role in some cellular environments.
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PMID:Cis- and trans-regulation of feline immunodeficiency virus: identification of functional binding sites in the long terminal repeat. 812 51

Feline immunodeficiency virus (FIV) causes progressive immunodeficiency in domestic cats, with clinical course dependent on virus strain. For example, clade A FIV-PPR is predominantly neurotropic and causes a mild disease in the periphery, whereas clade C FIV-C36 causes fulminant disease with CD4(+) T-cell depletion and neutropenia but no significant pathology in the central nervous system. In order to map pathogenic determinants, chimeric viruses were prepared between FIV-C36 and FIV-PPR, with reciprocal exchanges involving (i) the 3' halves of the viruses, including the Vif, OrfA, and Env genes; (ii) the 5' end extending from the 5' long terminal repeat (LTR) to the beginning of the capsid (CA)-coding region; and (iii) the 3' LTR and Rev2-coding regions. Ex vivo replication rates and in vivo replication and pathologies were then assessed and compared to those of the parental viruses. The results show that FIV-C36 replicates ex vivo and in vivo to levels approximately 20-fold greater than those of FIV-PPR. None of the chimeric FIVs recapitulated the replication rate of FIV-C36, although most replicated to levels similar to those of FIV-PPR. The rates of chloramphenicol acetyltransferase gene transcription driven by the FIV-C36 and FIV-PPR LTRs were identical. Furthermore, the ratios of surface glycoprotein (SU) to capsid protein (CA) in the released particles were essentially the same in the wild-type and chimeric FIVs. Tests were performed in vivo on the wild-type FIVs and chimeras carrying the 3' half of FIV-C36 or the 3' LTR and Rev2 regions of FIV-C36 on the PPR background. Both chimeras were infectious in vivo, although replication levels were lower than for the parental viruses. The chimera carrying the 3' half of FIV-C36 demonstrated an intermediate disease course with a delayed peak viral load but ultimately resulted in significant reductions in neutrophil and CD4(+) T cells, suggesting potential adaptation in vivo. Taken together, the findings suggest that the rapid-growth phenotype and pathogenicity of FIV-C36 are the result of evolutionary fine tuning throughout the viral genome, rather than being properties of any one constituent.
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PMID:Replication properties of clade A/C chimeric feline immunodeficiency viruses and evaluation of infection kinetics in the domestic cat. 1855 Jun 65