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)

The structural and enzymatic components of retroviral cores are formed by proteolytic cleavage of precursor polypeptides, mediated by the viral protease (PR). We constructed an active-site mutation, D37I, in the PR of avian leukosis virus. The D37I mutation was introduced into an infectious DNA clone, and quail cell lines expressing the mutant virus were established. These cell lines produce normal amounts of virus particles, the major internal protein components of which are the uncleaved gag and gag-pol precursors. As in other retroviral systems, the protease-defective virions are noninfectious and retain the "immature" type A morphology as determined by thin-section transmission electron microscopy. The virion cores are stable at nonionic detergent concentrations that completely disrupt wild-type cores. Digestion of mutant virions with exogenous PR in the presence of detergent leads to complete and correct cleavage of the gag precursor but incomplete cleavage of the gag-pol precursor. The protease-defective virions encapsidate normal amounts of genomic RNA and tRNA(Trp) that is properly annealed to the primer-binding site, but some of the genomic RNA remains monomeric. Results from UV cross-linking experiments show that the gag polyprotein of mutant virions interacts with viral RNA and that this interaction occurs through the nucleocapsid (NC) domain. However, within mutant virions the interaction of the NC domain with RNA differs from that of mature NC with RNA in wild-type virions. Reverse transcriptase (RT) activity associated with mutant virions is diminished but still detectable. Digestion of the virions with PR leads to a fivefold increase in activity, but this PR-mediated activation of RT is incomplete. Since in vitro cleavage of the gag-pol precursor is also incomplete, we hypothesize that amino acid sequences N terminal to the reverse transcriptase domain inhibit RT activity.
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PMID:Properties of avian retrovirus particles defective in viral protease. 169 12

The structural and enzymatic components of retroviral cores are formed by proteolytic cleavage of precursor polypeptides, mediated by the viral protease (PR). We described previously the construction of PR-defective avian leukosis viruses. These mutant viruses are noninfectious, and their major internal components are the uncleaved gag and gag-pol polyproteins (Pr76gag and Pr180gag-pol). The reverse transcriptase (RT) activity associated with the PR-defective virions is approximately 500-fold reduced relative to that of wild-type virions, suggesting that specific cleavages activate RT activity. To gain a better understanding of the role that PR plays in the processing and activation of RT, we performed complementation experiments wherein wild-type or PR mutant gag precursors were separately coexpressed with frame-corrected wild-type or PR mutant gag-pol precursors. The results demonstrate that, as in other retrovirus systems, gag-pol precursors can be assembled into virions only when they are rescued by a gag precursor. If the gag precursor is wild type, then the rescued Pr180gag-pol is completely and properly matured, irrespective of whether its embedded PR domain is wild type or mutant. In both cases, the virions produced are fully and equally infectious. This indicates that an active-site mutation in the PR domain of the gag-pol precursor has no effect on avian leukosis virus infectivity when particles are assembled from wild-type gag precursors. In contrast, if the gag precursor has an active-site mutation in PR or is deleted for PR, then the virions are noninfectious and the gag and gag-pol precursors remain unprocessed, even if the embedded PR domain of Pr180gag-pol is wild type. Thus, in this system, virion-associated Pr180gag-pol displays no detectable cis- or trans-acting PR activity. As assayed with an exogenous template, virions with processed gag-pol polyprotein display high levels of RT activity while those with unprocessed Pr180gag-pol display greatly reduced RT activity. These results demonstrate that during virion assembly, the PR supplied by a gag precursor is both necessary and sufficient for trans-activation of RT through proteolytic maturation of copackaged gag-pol polyprotein.
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PMID:trans-acting viral protease is necessary and sufficient for activation of avian leukosis virus reverse transcriptase. 171 19

We tested the ability of the thymidine analog 3'-azido-3'-deoxythymidine (BWA509U) to inhibit the replication of the retrovirus avian leukosis virus. Inhibition was measured with two different assays: inhibition of a single round of virus replication and inhibition of virus spread through a cell culture. With both assays, we detected inhibition of virus growth, although inhibition of a single round of virus replication required a 40-fold higher drug concentration than did inhibition of virus spread. We also detected variations in the concentrations of drug needed to inhibit virus replication in different cell types. Higher concentrations of drug were needed to inhibit virus replication in chicken embryo fibroblasts than in the continuous quail cell line QT6. Viral DNA synthesis in infected cells was shown to be inhibited in the presence of the drug. The triphosphate form of the analog acted as a competitive inhibitor of purified viral reverse transcriptase, with a Ki of 0.09 +/- 0.003 microM, and was incorporated as a chain terminator during reverse transcription of the natural viral RNA substrate in vitro.
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PMID:3'-Azido-3'-deoxythymidine inhibits the replication of avian leukosis virus. 244 Oct 79

We have analyzed transmission of (LTR, v-src, LTR) cryptic structure integrated in the H-19 mammalian tumor cell line. From this cell line different isolates of transforming virus were rescued in heterokaryons produced by fusion with chicken fibroblasts infected by replication-competent avian leukosis virus RAV-1. One of them (F6) was used for the transformation of avian cells in the absence of the helper virus. In four transformed cell lines studied, the (LTR, v-src, LTR) structure was again integrated at a unique position in the cell DNA of each line. This indicated that the (LTR, v-src, LTR) structure is transmitted by the helper virus without recombination. This point has been further supported by the finding that a src-containing species corresponding in size to the nonpolyadenylated src mRNA is present in the RNA isolated from the rescued F6 transforming virus which might serve as template for the synthesis of (LTR, v-src, LTR) structure by the reverse transcriptase provided by RAV-1.
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PMID:Transmission of (LTR, v-src, LTR) without recombination with a helper virus. 301 94

Antibodies against a large and a small DNA polymerase isolated from chicken embryos and against avian myeloblastosis virus DNA polymerase were used to study the serological relationships of the DNA polymerase activities of three avian systems with RNA and a DNA polymerase-avian leukosis-sarcoma viruses, reticuloendotheliosis viruses, and a fraction from uninfected chicken cells. The DNA polymerase activity of disrupted virions of all avian leukosis-sarcoma viruses tested was neutralized to the same extent by antibody against avian myeloblastosis virus DNA polymerase and was not neutralized by the antibodies against chicken cellular DNA polymerases. The viruses tested included induced leukosis viruses and Rous-associated virus-O. The DNA polymerase activity of disrupted virions of all of the reticuloendotheliosis viruses was not neutralized by any of the antibodies. The chicken endogenous RNA-directed DNA polymerase activity was neutralized partially or completely, in different experiments, by antibody against the small DNA polymerase isolated from chicken embryos, but was not neutralized by the other two antibodies.
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PMID:Lack of serological relationship among DNA polymerases of avian leukosis-sarcoma viruses, reticuloendotheliosis viruses, and chicken cells. 412 28

The relatedness of the RNAs of the three avian systems, including six avian leukosis-sarcoma viruses, four reticuloendotheliosis viruses, and the microsome fraction of normal uninfected chicken embryo cells, containing RNA and a DNA polymerase have been studied by nucleic acid hybridization. All six avian leukosis-sarcoma viruses have closely related nucleotide sequences; and all four reticuloendotheliosis viruses have closely related nucleotide sequences. But, almost no similarities were detected between the RNAs of avian leukosis-sarcoma viruses and reticuloendotheliosis viruses. The RNA template of the endogenous RNA-directed DNA polymerase activity of normal uninfected chicken cells had no detectable relationship to RNAs of avian leukosis-sarcoma and reticuloendotheliosis viruses.
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PMID:Lack of sequence homology among RNAs of avian leukosis-sarcoma viruses, reticuloendotheliosis viruses, and chicken endogenous RNA-directed DNA polymerase activity. 412 78

Early chicken embryos that are either positive or negative for group-specific antigens of avian leukosis viruses contained endogenous RNA-directed DNA polymerase activity. This endogenous DNA polymerase activity was not increased after mixture of soluble DNA polymerases isolated from chicken embryos with disrupted chicken embryo cells. The endogenous activity was resistant to treatment with deoxyribonuclease, and the initial rate of DNA synthesis was partially resistant to actinomycin D. In contrast, over 90% of the endogenous polymerase activity was destroyed by ribonuclease in medium with high salt concentration. The DNA product of the endogenous DNA polymerase activity from chicken embryos did not hybridize with RNA of Rous sarcoma virus or reticuloendotheliosis virus, whereas about 40% of this DNA product hybridized with the RNA from the same chicken-cell fraction. Antibody against DNA polymerase of avian myeloblastosis virus did not neutralize the chicken endogenous DNA polymerase activity. These results demonstrate that uninfected chicken embryo cells contain endogenous RNA-directed DNA polymerase activity that is not derived from avian leukosis or reticuloendotheliosis viruses.
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PMID:Endogenous RNA-directed DNA polymerase activity in uninfected chicken embryos. 433 97

Stationary chicken embryo fibroblasts exposed to Rous sarcoma virus (RSV) remained stably infected for at least 5 days, but they did not release infectious virus or become transformed until after cell division. These infected stationary cells did not contain avian leukosis virus group-specific antigens or ribonucleic acid (RNA) hybridizable to deoxyribonucleic acid (DNA) made by the RSV endogenous RNA-directed DNA polymerase activity.
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PMID:Cell cycle-dependent activation of rous sarcoma virus-infected stationary chicken cells: avian leukosis virus group-specific antigens and ribonucleic acid. 433 98

Five techniques were compared for their ability to detect decreasing dilutions of RAV-I, an avian leukosis sarcoma virus, in serially passaged chick embryo fibroblast cell cultures. The indirect fluorescent antibody test, sandwich enzyme-linked immunosorbent assay (ELISA) and reverse transcriptase assay were equally sensitive in detecting the virus. The indirect immunoperoxidase and complement fixation avian leukosis tests were less sensitive. It is recommended that the sandwich ELISA be used for routine detection of the avian leukosis sarcoma virus group as possible vaccine contaminants because it is rapid and simple to perform and may be carried out on a large number of samples conveniently.
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PMID:Detection of avian leukosis virus: comparison of five techniques. 608 74

125I-labeled DNA polymerases of avian myeloblastosis virus and spleen necrosis virus were used in a radioimmunological characterization of avian retrovirus DNA polymerases. It was shown that avian leukosis virus and reticuloendotheliosis virus DNA polymerases do not cross-react in radioimmunoassays. Within the avian leukosis virus species, species-specific and type-specific antigenic determinants of the DNA polymerase were defined. The previous finding of genus-specific antigenic determinants in avian myeloblastosis virus and Amherst pheasant virus DNA polymerases was confirmed and extended to members of all subgroups of avian leukosis virus. It was shown that there is little immunological variation between the DNA polymerases of the four members of the reticuloendotheliosis virus species. Particles with RNA-dependent DNA polymerase activity from the allantoic fluid of normal chicken eggs and from the medium of a goose cell culture did not compete for the antibodies directed against any of the sets of antigenic determinants defined in this study.
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PMID:Radioimmunological comparison of the DNA polymerases of avian retroviruses. 615 53


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