Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0023418 (leukemia)
 93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previous work indicates that hepatitis B virus (HBV) and retroviruses utilize a unique mechanism for genome replication by reverse transcription of RNA and share homology in biologically important nucleotide and protein sequences. The data presented here extend previous findings of sequence homology among the genomes of the members of these virus families. HBV was found to possess sequences homologous to the retrovirus protease and reverse transcriptase gene sequences. Homology was not found to the retrovirus integrase sequence consistent with the observation that hepadnaviruses do not integrate into cellular DNA as a necessary step in their replication cycle. Overall, the homology of the hepadnavirus polymerase gene was strongest with that of the murine leukemia viruses (MLVs). Also, the hepadnavirus polymerase shares organizational similarities to the MLV polymerase sequence. Analysis suggests that the ancestor of both hepadnaviruses and retroviruses possessed an overlapping long open reading frame in the polymerase gene sequence. In addition, low stringency blot hybridization using hepadnavirus DNA probes indicates that HBV is more closely related to MLV sequences than the sequences of MLV-related viruses and endogenous retrovirus-like genetic elements. Taken together, the data indicate that the polymerase gene sequence of the hepadnavirus and MLV genomes are organized in a similar fashion which suggests that these viruses evolved from a common ancestor.
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PMID:Close evolutionary relatedness of the hepatitis B virus and murine leukemia virus polymerase gene sequences. 245 12

An insertion mutation in the pol gene of Moloney murine leukemia virus (M-MuLV) was found to render the virus temperature-sensitive for replication. A provirus containing a 12-bp insertion at the boundary between the reverse transcriptase (RT) and integrase (IN) domains induced the formation of mutant virions containing a partially processed RT-IN fusion protein. Some proteolytic processing to form mature RT and IN was observed at 32 degrees, but only aberrantly processed proteins were detected at 39 degrees. The uncleaved precursor was found to exhibit DNA polymerase activity, even though it could not support replication of the virus in vivo at 39 degrees.
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PMID:An insertion mutation in the pol gene of Moloney murine leukemia virus results in temperature-sensitive pol maturation and viral replication. 278 80

Feline leukemia virus (FeLV) C-Sarma (or FSC) is a prototype of subgroup C FeLVs, which induce fatal aplastic anemia in outbred specific-pathogen-free (SPF) cats. FeLV C isolates also possess an extended host range in vitro, including an ability, unique among FeLVs, to replicate in guinea pig cells. To identify the viral determinants responsible for the pathogenicity and host range of FSC we constructed a series of proviral DNAs by exchanging gene fragments between FSC and FeLV-61E (or F6A), the latter of which is minimally pathogenic and whose host range in vitro is restricted to feline cells. Transfer of an 886-base-pair (bp) fragment of FSC, encompassing the codons for 73 amino acids at the 3' end of pol (the integrase/endonuclease gene) and the codons for 241 amino acids of the N-terminal portion of env [the extracellular glycoprotein (gp70) gene], into the F6A genome was sufficient to confer onto chimeric viruses the ability to induce fatal aplastic anemia in SPF cats. In contrast, no chimera lacking this sequence induced disease. When assayed in vitro, all chimeric viruses containing the 886-bp fragment of FSC acquired the ability to replicate in heterologous cells, including dog and guinea pig cells. Thus, the pathogenic and the host range determinants of the feline aplastic anemia retrovirus colocalize to a 3' pol-5' env region of the FSC genome and likely reside within a region encoding 241 amino acid residues of the N terminus of the extracellular glycoprotein.
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PMID:Pathogenic and host range determinants of the feline aplastic anemia retrovirus. 283 51

The murine AIDS (MAIDS) virus has a unique sequence in the gag p12 region, which could be responsible for MAIDS development. RNA preparations from the spleens of normal uninfected C57BL/6 mice contain a transcript hybridizing with this sequence. Levels of the transcript in the kidney of C57BL/6 mice were higher than in the spleen, liver or thymus. Although BALB/c, NFS, DBA/2 and SL murine strains also contained genomic sequences hybridizing with the MAIDS virus-specific probe, no transcript hybridizing with the probe was detected in these strains of mice. The cDNAs carrying the transcript expressed in C57BL/6 mice were molecularly cloned. The complete nucleotide sequence of the clone indicates that the transcript is one of the endogenous murine leukaemia virus-related sequences containing large deletions from the R and U5 regions of the 5' long terminal repeat (LTR) to gag p15, from the C-terminal region of pol p40 (integrase) to the N-terminal region of env p15E, and many short deletions in the 3' LTR U3 region. The nucleotide sequence in the gag p12 region of the transcript was closely similar to that of the MAIDS virus, but the amino acid sequence was less similar because of frameshifting, even when translated. As the MAIDS virus was isolated from C57BL/6 mice with radiation-induced leukaemia, this transcript may be the progenitor of the MAIDS virus. To determine whether the gag p12 region of the transcript contains a functional sequence, a recombinant virus was generated by replacing the gag p12 region of a replication-competent BM5eco virus with that of the endogenous transcript. The recombinant virus was replication-competent, and the p12 region of the transcript retained the functional sequence present in the BM5eco virus.
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PMID:Molecular cloning and characterization of a murine AIDS virus-related endogenous transcript expressed in C57BL/6 mice. 751 20

We generated variants of the human immunodeficiency virus type 1 (HIV-1) that are resistant to 2',3'-dideoxycytidine (ddC) and 2',3'-didehydro-3'-deoxythymidine (d4T) by in vitro selection in MT-4 cells. Portions of flanking protease and integrase sequences as well as the complete reverse transcriptase (RT) open-reading frame of these viruses were cloned and sequenced, using polymerase chain reaction (PCR)-based methods. Mutations were observed at amino acid position 65 (Lys-->Arg; AAA-->AGA) when ddC was employed in the selection procedure and at site 50 (Ile-->Thr; ATT-->ACT) when d4T was used. We confirmed the ability of these mutations to confer diminished sensitivity for these compounds by site-directed mutagenesis, in which these mutations were inserted into the pol gene of infectious recombinant HXB2-D DNA. Viruses that contained the site 65 mutation possessed approximately 5-10 fold resistance against ddC when compared with wild-type HXB2-D. The site 50 mutation conferred approximately 30-fold resistance to d4T in these same assays. Similar results were obtained using primary cord blood lymphocytes in drug resistance assays, indicating that these mutations could confer drug resistance in more than one cell type and that the respective mutations could be expressed in cells of primary origin. No cross-resistance against 3'-azido-3'-deoxythymidine (AZT) was noted for either the site 65 or 50 mutations.
Leukemia 1994 Apr
PMID:Identification of novel mutations that confer drug resistance in the human immunodeficiency virus polymerase gene. 751 78

The possible intervention of nuclear proteins as cofactors of integrase-catalyzed integration of retroviral DNA into the host cell genome is not fully understood. Among various nuclear proteins, DNA topoisomerase II appears to be a plausible candidate. This hypothesis is supported by a series of evidence, including the fact that integration is markedly affected by the topology of the target DNA and mainly occurs in transcribed regions in which topoisomerase II is preferentially located. In an attempt to confirm the validity of this hypothesis, we have comparatively investigated the early stages of a recombinant Moloney murine leukemia virus (psi neo) in two related Chinese hamster cell lines (DC3F and R/DC3F) expressing different levels of both isoforms of topoisomerase II. R/DC3F is derived from the parental cell line DC3F and displays a resistant phenotype towards the usual anticancer topoisomerase II inhibitors (actinomycin D, doxorubicin, and taxol). Results show that the early stages of the retroviral cycle are markedly impaired in cells underexpressing topoisomerase II (R/DC3F). This alteration mimics Fv-1 restriction and is characterized by about a 6-fold decrease in viral DNA synthesis and total inhibition of viral genome integration. The specific impairment of integration in R/DC3F cells compared to DC3F cells is assessed by the absence of G418-resistant colonies upon viral infection and a lack of the viral genome in cellular nuclear DNA as detected by the PCR procedure. These features are observed in relevant infecting conditions leading, in both cell lines, to the same amount of linear viral DNA and to the occurrence of two long terminal repeats containing circular DNA in the nuclear fractions.
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PMID:Impairment of Moloney murine leukemia virus integration in a cell line underexpressing DNA topoisomerase II. 760 43

Retroviral DNA synthesis requires both the DNA polymerase and the RNaseH activities of reverse transcriptase (RT). To test whether two defective RTs--one carrying a mutation in the RNaseH domain and the other with a mutation in DNA polymerase--could work together to complete viral DNA synthesis, we generated phenotypically mixed virions of Moloney murine leukemia virus (M-MuLV) that contained two kinds of mutant RTs. One RNaseH catalytic site mutant complemented both tested DNA polymerase mutants and small amounts of intact viral DNA were generated. This demonstrates that retroviral DNA synthesis can be completed--albeit inefficiently--when DNA polymerase and RNaseH activities are provided by separate RT molecules. Other RNaseH mutants failed to complement, suggesting that some aspects of the RNaseH domain are essential to RT's DNA polymerase function. Phenotypically mixed virions were also used to demonstrate that RT and integrase (IN) can be provided by separate polyprotein precursors and complete the early stages of retroviral replication.
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PMID:Two defective forms of reverse transcriptase can complement to restore retroviral infectivity. 769 56

Integration of retroviral DNA involves a coordinated joining of the two ends of a viral DNA molecule into precisely spaced sites on target DNA. In this study, we designed an assay that requires two separate oligonucleotides to be brought together via interactions between integrase promoters to form a "crossbones" substrate that mimics the integration intermediate. The crossbones substrate contains two viral DNA ends, each joined to one strand of target DNA and separated by a defined length of target DNA. We showed that purified integrases of human immunodeficiency virus type 1 (HIV-1) and murine leukemia virus (MLV) could mediate a concerted strand cleavage-ligation between the two half-substrates at one or both viral DNA joining sites (trans disintegration). Another major product, termed fold-back, resulted from an intramolecular attack on the phosphodiester bond at the viral-target DNA junction by the 3'-OH group of the same DNA molecule (cis disintegration). The activity of integrase on the crossbones substrate depended on the presence of viral DNA sequences. For trans disintegration, the optimal length of target DNA between the viral DNA joining sites of the crossbones substrate corresponded to the spacing between the staggered joints formed on two opposite strands of target DNA during retroviral DNA integration in vivo. The activity of integrases on crossbones did not require complementary base pairing between the two half-substrates, indicating that the half-substrates were juxtaposed solely through protein-DNA interactions. The crossbones assay, therefore, measures the ability of integrase to juxtapose two viral DNA ends, an activity which heretofore has been difficult to detect by using purified integrase in conventional assays. Certain mutant integrases that were otherwise inactive with the crossbones substrate could complement one another, indicating that no single protomer in the integrase multimer requires a complete set of functional domains either for catalytic activity or for juxtaposition of the two viral DNA ends by the active multimer.
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PMID:Juxtaposition of two viral DNA ends in a bimolecular disintegration reaction mediated by multimers of human immunodeficiency virus type 1 or murine leukemia virus integrase. 796 77

Retroviral integration involves two DNA substrates that play different roles. The viral DNA substrate is recognized by virtue of specific nucleotide sequences near the end of a double-stranded DNA molecule. The target DNA substrate is recognized at internal sites with little sequence preference; nucleosomal DNA appears to be preferred for this role. Despite this apparent asymmetry in the sequence, structure, and roles of the DNA substrates in the integration reaction, the existence of distinct binding sites for viral and target DNA substrates has been controversial. In this report, we describe the expression in Escherichia coli and purification of Moloney murine leukemia virus integrase as a fusion protein with glutathione S-transferase, characterization of its activity by using several model DNA substrates, and the initial kinetic characterization of its interactions with a model viral DNA substrate. We provide evidence for functionally and kinetically distinct binding sites for viral and target DNA substrates and describe a cross-linking assay for DNA binding at a site whose specificity is consistent with the target DNA binding site.
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PMID:Characterization of recombinant murine leukemia virus integrase. 798 42

Retroviral DNA integration requires the activity of at least one viral protein, the integrase (IN) protein. We cloned and expressed the integrase gene of feline immunodeficiency virus (FIV) in Escherichia coli as a fusion to the malE gene and purified the IN fusion protein by affinity chromatography. The protein is active in site-specific cleavage of the viral DNA ends, DNA strand transfer, and disintegration. FIV IN has a relaxed viral DNA substrate requirement: it cleaves and integrates FIV DNA termini, human immunodeficiency virus DNA ends, and Moloney murine leukemia virus DNA ends with high efficiencies. In the cleavage reaction, IN exposes a specific phosphodiester bond near the viral DNA end to nucleophilic attack. In vitro, either H2O, glycerol, or the 3' OH group of the viral DNA terminus can serve as nucleophile in this reaction. We found that FIV IN preferentially uses the 3' OH ends of the viral DNA as nucleophile, whereas HIV IN protein preferentially uses H2O and glycerol as nucleophiles.
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PMID:Activities of the feline immunodeficiency virus integrase protein produced in Escherichia coli. 810 10


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