Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.49 (reverse transcriptase)
 31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Uracilation of DNA represents a constant threat to the survival of many organisms including viruses. Uracil may appear in DNA either by cytosine deamination or by misincorporation of dUTP. The HIV-1-encoded Vif protein controls cytosine deamination by preventing the incorporation of host-derived APOBEC3G cytidine deaminase into viral particles. Here, we show that the host-derived uracil DNA glycosylase UNG2 enzyme, which is recruited into viral particles by the HIV-1-encoded integrase domain, is essential to the viral life cycle. We demonstrate that virion-associated UNG2 catalytic activity can be replaced by the packaging of heterologous dUTPase into virion, indicating that UNG2 acts to counteract dUTP misincorporation in the viral genome. Therefore, HIV-1 prevents incorporation of dUTP in viral cDNA by UNG2-mediated uracil excision followed by a dNTP-dependent, reverse transcriptase-mediated endonucleolytic cleavage and finally by strand-displacement polymerization. Our findings indicate that pharmacologic strategies aimed toward blocking UNG2 packaging should be explored as potential HIV/AIDS therapeutics.
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PMID:HIV-1-associated uracil DNA glycosylase activity controls dUTP misincorporation in viral DNA and is essential to the HIV-1 life cycle. 1572 Dec 52

Retrotransposons are suitable targets for developing molecular markers for population genetics studies. Transposable elements have not yet been isolated from ectomycorrhizal fungi of the genus Tuber. In this paper, we report on the isolation and characterization of Tmt1, an LTR-retrotransposon from Tuber melanosporum. The Tmt1 sequence shows relatedness to Ty3/gypsy retrotransposons from which it differentiates for the presence of a dUTPase extra-domain between protease and reverse transcriptase. Phylogenetic analyses suggest a horizontal transfer of the dUTPase gene (dut) from a fungal host genome. The presence of non-identical LTRs and degenerate ORFs substantiate an ancient integration of Tmt1 in T. melanosporum genome. Furthermore, transcripts analyses proved an inactive status of Tmt1, whereas Southern analysis showed that Tmt1 is a repetitive T. melanosporum species-specific element. Tmt1-based markers will help us to gain more insights into population biology in this fungal species.
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PMID:Tmt1: the first LTR-retrotransposon from a Tuber spp. 1797 80

The highly divergent, small ruminant lentivirus (SRLV) genotype E Roccaverano strain has a full genome consisting of 8,418 nucleotides, which lack the entire dUTPase subunit of the pol gene, the vpr-like accessory gene, and the 71-bp repeat of the U3 region within the long terminal repeat (LTR). These deletions affect in reverse transcriptase fidelity in non-dividing cells (dUTPase and vpr-like) and in the regulation of viral replication. Surprisingly, this SRLV strain was able to replicate efficiently in non-dividing cells (i.e., blood-derived macrophages), while replication in fibroblastic-like cells was somewhat restricted. To evaluate whether this observation was due to the presence/absence of specific transcription factors within these fibroblasts, U3 transcriptional activity was measured in the different cell types and revealed that both fibroblasts and macrophages were able to activate the viral promoter in the same manner. Among the transcription factor-binding sites present within the U3 region, the highly conserved Ap4 tandem repeat was shown to be sufficient for LTR promoter activity.
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PMID:LTR promoter activity of SRLV genotype E, strain Roccaverano. 2048 Feb 32

Human immune cells infected by HIV naturally contain high uracil content, and HIV reverse transcriptase (RT) does not distinguish between dUTP and dTTP. Many DNA viruses and retroviruses encode a dUTPase or uracil-DNA glycosylase (UNG) to counteract uracil incorporation. However, although HIV virions are thought to contain cellular UNG2, replication of HIV produced in cells lacking UNG activity does not appear to be impaired. Here we show that HIV reverse transcripts generated in primary human immune cells are heavily uracilated (>500 uracils per 10 kb HIV genome). We find that HIV DNA uracilation, rather than being dangerous, may promote the early phase of the viral life cycle. Shortly after reverse transcription, the ends of the HIV DNA are activated by the viral integrase (IN) in preparation for chromosomal insertion. However, the activated ends can attack the viral DNA itself in a suicidal side pathway, called autointegration. We find here that uracilation of target DNA inhibits the strand transfer of HIV DNA ends by IN, thereby inhibiting autointegration and facilitating chromosomal integration and viral replication. When uracilation is increased by incubating uracil-poor cells in the presence of increasing concentrations of dUTP or by infecting with virus that contains the cytosine deaminase APOBEC3G (A3G), the proportion of reverse transcripts that undergo suicidal autointegration decreases. Thus, HIV tolerates, or even benefits from, nonmutagenic uracil incorporation during reverse transcription in human immune cells.
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PMID:HIV DNA is heavily uracilated, which protects it from autointegration. 2157 78

HIV-1 reverse transcriptase discriminates poorly between dUTP and dTTP, and accordingly, viral DNA products become heavily uracilated when viruses infect host cells that contain high ratios of dUTP:dTTP. Uracilation of invading retroviral DNA is thought to be an innate immunity barrier to retroviral infection, but the mechanistic features of this immune pathway and the cellular fate of uracilated retroviral DNA products is not known. Here we developed a model system in which the cellular dUTP:dTTP ratio can be pharmacologically increased to favor dUTP incorporation, allowing dissection of this innate immunity pathway. When the virus-infected cells contained elevated dUTP levels, reverse transcription was found to proceed unperturbed, but integration and viral protein expression were largely blocked. Furthermore, successfully integrated proviruses lacked detectable uracil, suggesting that only nonuracilated viral DNA products were integration competent. Integration of the uracilated proviruses was restored using an isogenic cell line that had no detectable human uracil DNA glycosylase (hUNG2) activity, establishing that hUNG2 is a host restriction factor in cells that contain high dUTP. Biochemical studies in primary cells established that this immune pathway is not operative in CD4+ T cells, because these cells have high dUTPase activity (low dUTP), and only modest levels of hUNG activity. Although monocyte-derived macrophages have high dUTP levels, these cells have low hUNG activity, which may diminish the effectiveness of this restriction pathway. These findings establish the essential elements of this pathway and reconcile diverse observations in the literature.
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PMID:Uracil DNA glycosylase initiates degradation of HIV-1 cDNA containing misincorporated dUTP and prevents viral integration. 2334 16

The complete genome of the Piper yellow mottle virus (PYMoV), a Badnavirus belonging to the family Caulimoviridae, was sequenced from three naturally infected hosts namely, black pepper, betelvine, and Indian long pepper. The genome length of the three virus strains (one from each of the three host species) varied from 7,559 to 7,584 nucleotides, and all the three strains possessed four open reading frames (ORFs) I to IV that potentially encode proteins of 15.67, 17.08, 218.6, and 17.22 kDa, respectively. ORF III encodes a polyprotein consisting of viral movement protein, trimeric dUTPase, zinc finger, aspartic protease, reverse transcriptase, and RNase H whereas ORF I, II, and IV encode proteins of unknown functions. The complete genome sequences at the nucleotide level were 89-99 % identical with one available sequence of PYMoV and 39-56 % identical with other badnaviruses, indicating that all three are strains of PYMoV. Nucleotide and amino acid sequences of ORF I-IV and of the intergenic region (IR) were 80-100 % identical among PYMoV strains. Phylogenetic analysis of ORF III amino acid sequences showed the PYMoV strains forming a distinct cluster well separated from other badnaviruses. Among other badnaviruses, Fig badnavirus 1 (FBV-1) was the one most closely related to PYMoV.
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PMID:Complete genome sequencing of Piper yellow mottle virus infecting black pepper, betelvine, and Indian long pepper. 2533 43

Retroviruses are among the best studied viruses in last decades due to their pivotal involvement in cellular processes and, most importantly, in causing human diseases, most notably-acquired immunodeficiency syndrome (AIDS) that is triggered by human immunodeficiency viruses types 1 and 2 (HIV-1 and HIV-2, respectively). Numerous studied were conducted to understand the involvement of the three cardinal retroviral enzymes, reverse transcriptase, integrase and protease, in the life cycle of the viruses. These studies have led to the development of many inhibitors of these enzymes as anti-retroviral specific drugs that are used for routine treatments of HIV/AIDS patients. Interestingly, a fourth virus-encoded enzyme, the deoxyuridine 5'-triphosphate nucleotidohydrolase (dUTPase) is also found in several major retroviral groups. The presence and the importance of this enzyme to the life cycle of retroviruses were usually overlooked by most retrovirologists, although the occurrence of dUTPases, particularly in beta-retroviruses and in non-primate retroviruses, is known for more than 20 years. Only more recently, retroviral dUTPases were brought into the limelight and were shown in several cases to be essential for viral replication. Therefore, it is likely that future studies on this enzyme will advance our knowledge to a level that will allow designing novel, specific and potent anti-dUTPase drugs that are effective in combating retroviral diseases. The aim of this review is to give concise background information on dUTPases in general and to summarize the most relevant data on retroviral dUTPases and their involvement in the replication processes and pathogenicity of the viruses, as well as in possibly-associated human diseases.
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PMID:dUTPase: the frequently overlooked enzyme encoded by many retroviruses. 2637 May 46


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