Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.6 (RNA polymerase)
 34,946 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.
 ...
PMID:Properties of avian retrovirus particles defective in viral protease. 169 12

The interesting possibility that transcriptional interference can occur between eukaryotic genes was raised by studies on the avian leukosis retrovirus (ALV) which showed that deletion of the promoter in the 5' long terminal repeat (LTR) activates the 3' LTR promoter, linked to a downstream gene. These observations provide a molecular explanation for the fact that insertional oncogenesis by the ALV promoter is invariably associated with either a rearranged or deleted 5' LTR sequence. This letter extends these findings to chromosomal RNA polymerase II genes by studying transcriptional interference between duplicated alpha-globin gene constructions. I demonstrate that transcriptional interference causes substantial inhibition of the downstream alpha gene by transcription of the upstream alpha gene. Furthermore, this inhibition is alleviated by placing transcriptional termination signals between the two alpha genes. Because many eukaryotic genes may be arranged in tandem on a chromosome, these observations suggest that transcriptional termination is an important mechanism for preventing interference between adjacent genes. The selective use of termination signals may provide a novel way of regulating the activity of eukaryotic genes.
 ...
PMID:Transcriptional interference and termination between duplicated alpha-globin gene constructs suggests a novel mechanism for gene regulation. 373 74

Influenza virus infection has adverse effects on the metabolism of two representative RNA polymerase II transcripts in chicken embryo fibroblasts, those coding for beta-actin and for avian leukosis virus (ALV) proteins. Proviral ALV DNA was integrated into host cell DNA by prior infection with ALV. Within 1 h after influenza virus infection, the rate of transcription of beta-actin and ALV sequences decreased 40 to 60%, as determined by labeling the cells for 5 min with [3H]uridine and by in vitro, runoff assays with isolated nuclei. The transcripts that continued to be synthesized did not appear in the cytoplasm as mature mRNAs, and the kinetics of labeling of these transcripts strongly suggest that they were degraded in the nucleus. By S1 endonuclease assay, it was confirmed that nuclear ALV transcripts disappeared very early after infection, already decreasing ca. 80% by 1 h postinfection. A plausible explanation for this nuclear degradation is that the viral cap-dependent endonuclease in the nucleus cleaves the 5' ends of new polymerase II transcripts, rendering the resulting decapped RNAs susceptible to hydrolysis by cellular nucleases. In contrast to the nuclear transcripts, cytoplasmic beta-actin and ALV mRNAs, which are synthesized before infection, were more stable and did not decrease in amount until after 3 h postinfection. Similar stability of cytoplasmic host cell mRNAs was observed in infected HeLa cells, in which the levels of actin mRNA and two HeLa cell mRNAs (pHe 7 and pHe 28) remained at undiminished levels for 3 h of infection and decreased only slightly by 4.5 h postinfection. The cytoplasmic actin and pHe 7 mRNAs isolated from infected HeLa cells were shown to be translated in reticulocyte extracts in vitro, indicating that host mRNAs were not inactivated by a virus-induced modification. Despite the continued presence of high levels of functional host cell mRNAs, host cell protein synthesis was effectively shut off by about 3 h postinfection in both chicken embryo fibroblasts and HeLa cells. These results are consistent with the establishment of an influenza virus-specific translational system that selectively translates viral and not host mRNAs.
 ...
PMID:Metabolism and expression of RNA polymerase II transcripts in influenza virus-infected cells. 609 46

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.
 ...
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.
 ...
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.
 ...
PMID:Histopathological characteristics of spindle-cell proliferative disease in broiler chickens and its experimental reproduction in specific pathogen-free chickens. 1510 49

Previous investigations have estimated the human immunodeficiency virus type 1 (HIV) base pair substitution rate to be approximately 10(-4) to 10(-5) per round of viral replication, and HIV has been hypothesized to be more error-prone than other retroviruses. Using a single cycle reversion assay, we unexpectedly found that the reversion rates of HIV, avian leukosis virus and Moloney murine leukemia virus were the same, within statistical error. Because both the viral enzyme reverse transcriptase (RT) and cellular RNA polymerase II (RNAP) are required for viral replication, we hypothesized that the similar reversion rates actually reflect the intrinsic error rate of RNAP, which is the enzyme common to all three retroviruses in the reversion assay. To address this possibility, HIV vectors with the U3 region replaced by a reporter reversion cassette were constructed and vector supernatant produced by transient transfection. All single integrant revertant cell lines showed the identical mutations at both long terminal repeats. This indicates that either RNAP or another cellular enzyme is responsible for these reversions, or that HIV RT only makes errors during first strand synthesis. Additionally, when HIV particles were rescued from an integrated vector as opposed to being produced by transient transfection, the reversion rate was significantly lower, suggesting that one or more factors in the virus-producing cells plays a role in the fidelity of retroviral replication. These results have implications regarding the fidelity of the transgene after transient transfection production of lentiviral vector supernatants.
 ...
PMID:Replicative fidelity of lentiviral vectors produced by transient transfection. 1646 44

To date, the vast majority of known virus-encoded microRNAs (miRNAs) are derived from polymerase II transcripts encoded by DNA viruses. A recent demonstration that the bovine leukemia virus, a retrovirus, uses RNA polymerase III to directly transcribe the pre-miRNA hairpins to generate viral miRNAs further supports the common notion that the canonical pathway of miRNA biogenesis does not exist commonly among RNA viruses. Here, we show that an exogenous virus-specific region, termed the E element or XSR, of avian leukosis virus subgroup J (ALV-J), a member of avian retrovirus, encodes a novel miRNA, designated E (XSR) miRNA, using the canonical miRNA biogenesis pathway. Detection of novel microRNA species derived from the E (XSR) element, a 148-nucleotide noncoding RNA with hairpin structure, showed that the E (XSR) element has the potential to function as a microRNA primary transcript, demonstrating a hitherto unknown function with possible roles in myeloid leukosis associated with ALV-J.
...
PMID:An avian retrovirus uses canonical expression and processing mechanisms to generate viral microRNA. 2415 81