Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.48 (transcriptase)
 9,479 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

A temperature-sensitive mutant (LA83) of Rous sarcoma virus defective both in the transformation and replication function has been isolated and partially characterized. Temperature-shift experiments showed that the defects in both the focus-forming and replication functions were late and continuous. The mutant LA83 was complemented by avian leukosis viruses. Complementation of LA83 replication was also observed with the glycoprotein-deletion mutant, Brian high-titer RSV(-) suggesting that the env gene in LA83 was not defective. At the nonpermissive temperature LA83-infected cells produced noninfectious particles with a yield of about 30%. The noninfectious particles had only about 3% of reverse-transcriptase activity as the infectious LA83 produced at the permissive temperature. However, the LA83 virions were as thermolabile as the parent wild-type PR-B virions.
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PMID:Characterization of a replication-defective temperature-sensitive mutant of Rous sarcoma virus. 620 47

Reverse transcriptase (RT) activity has been detected recently in all chicken cell-derived measles and mumps vaccines. A study of a vaccine manufactured in Europe indicated that the RT is associated with particles containing endogenous avian retrovirus (EAV-0) RNA and originates from the chicken embryonic fibroblasts (CEF) used as a substrate for propagation of the vaccine. We investigated the origin of RT in measles and mumps vaccines from a U.S. manufacturer and confirm the presence of RT and EAV RNA. Additionally, we provide new evidence for the presence of avian leukosis virus (ALV) in both CEF supernatants and vaccines. ALV pol sequences were first identified in particle-associated RNA by amplification with degenerate retroviral pol primers. ALV RNA sequences from both the gag and env regions were also detected. Analysis of hypervariable region 2 of env revealed a subgroup E sequence, an endogenous-type ALV. Both CEF- and vaccine-derived RT activity could be blocked by antibodies to ALV RT. Release of ALV-like virus particles from uninoculated CEF was also documented by electron microscopy. Nonetheless, infectivity studies on susceptible 15B1 chicken cells gave no evidence of infectious ALV, which is consistent with the phenotypes of the ev loci identified in the CEF. PCR analysis of ALV and EAV proviral sequences in peripheral blood mononuclear cells from 33 children after measles and mumps vaccination yielded negative results. Our data indicate that the sources of RT activity in all RT-positive measles and mumps vaccines may not be similar and depend on the particular endogenous retroviral loci present in the chicken cell substrate used. The present data do not support transmission of either ALV or EAV to recipients of the U.S.-made vaccine and provide reassurance for current immunization policies.
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PMID:Evidence of avian leukosis virus subgroup E and endogenous avian virus in measles and mumps vaccines derived from chicken cells: investigation of transmission to vaccine recipients. 1036 36

The livers and spleens of 45 broiler chickens (33 to 79 days old) suspected of Marek's disease (MD) at meat inspection were collected and examined histopathologically. Macroscopically, they were enlarged from two to three times, and multiple, small, white areas of plaque or infrequent, large, white nodules were observed in most cases. Only 9 birds (20%) were diagnosed with MD based on the histological examination, while the other 35 birds (78%) had tumor-like proliferative lesions in the Glisson's sheath of the liver and in the white pulp and around the sheathed arteries of the spleen, which differs from the pattern seen in MD. The proliferating cells were mainly spindle-shaped or pleomorphic, and were variable in size with abundant eosinophilic cytoplasm. The disease giving rise to the present lesions was diagnosed tentatively as spindle-cell proliferative disease. Total 50 1-day-old specific pathogen-free chicks by serial passage were inoculated intramuscularly with 0.1 ml of a 10% homogenate of the affected livers or spleens. Microscopically, one inoculated bird, necropsied at 6 weeks of age, had spindle-cell proliferative lesions in the spleen similar to the lesions of naturally occurring spindle-cell proliferative disease. Some birds had tumorous lesions, including renal adenoma, leiomyosarcoma and myxosarcoma. Reverse transcriptase-polymerase chain reaction performed using primers specific for subgroup J avian leukosis virus (ALV) produced specific amplifications of subgroup J ALV genes in 4 of 5 field cases examined.
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PMID:Histopathological characteristics of spindle-cell proliferative disease in broiler chickens and its experimental reproduction in specific pathogen-free chickens. 1510 49