Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

Giardiavirus is a small, nonenveloped virus comprising a monopartite double-stranded RNA genome, a major protein of 100 kDa, and a less abundant polypeptide of 190 kDa. It can be isolated from the culture supernatant of Giardia lamblia, a parasitic flagellate in human and other mammals, and efficiently infects other virus-free G. lamblia. A single-stranded copy of the viral RNA can be electroporated into uninfected G. lamblia cells to complete the viral replication cycle. Giardiavirus genomic cDNA of 6100 nt was constructed and its sequence revealed the presence of two large open reading frames that are separated by a -1 frameshift and share an overlap of 220 nt. The 3' open reading frame contains all consensus RNA-dependent RNA polymerase sequence motifs. A heptamer-pseudoknot structure similar to those found at ribosomal slippage sites in retroviruses and yeast killer virus was identified within this overlap. Immunostudies using antisera against synthesized peptides from four regions in the two open reading frames indicated that the 100- and 190-kDa viral proteins share a common domain in the amino-terminal region. But the 190-kDa protein makes a -1 switch of its reading frame beyond the presumed slippage heptamer and is therefore a -1 frameshift fusion protein similar to the gag-pol fusion protein found in retroviruses.
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PMID:Giardiavirus double-stranded RNA genome encodes a capsid polypeptide and a gag-pol-like fusion protein by a translation frameshift. 837 34

Two double-stranded RNA viruses exist as permanent persistent infections of the yeast Saccharomyces cerevisiae: ScVL1 and ScVLa. Both belong to the Totiviridae, which include a number of fungal and protozoan double-stranded RNA viruses. Although ScVL1 and ScVLa share the same genomic organization and mode of expression and coexist in the same cells, they show no evidence of recombination: with one limited exception, sequence conservation is detectable only in regions conserved in all totiviruses. Both have two open reading frames on their single essential RNAs: cap (encoding a capsid polypeptide) and pol (encoding an RNA-dependent RNA polymerase). The ScVLa virus, like ScVL1, appears to express its Pol domain by a -1 translational frameshift.
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PMID:A second double-stranded RNA virus from yeast. 860 77

The possible involvement of the human T lymphotropic viruses type I and II (HTLV-I and -II) in lymphoproliferative disorders of mature T cells other than adult T cell leukemia/lymphoma (ATLL) has been controversial. Most studies have focused primarily on the cutaneous T cell lymphomas. However, skin involvement is a frequent feature of T prolymphocytic leukemia (T-PLL) and antibodies against HTLV-I and -II have been reported in individuals with large granular lymphocytic (LGL) leukemia. We examined 36 patients with T-PLL and 28 with LGL leukemia for evidence of HTLV-I and -II. Polymerase chain reaction (PCR) was performed on DNA from fresh peripheral blood mononuclear cells (PBMCs) and PBMCs after short-term culture (STC) using primers against all parts of the HTLV-I genome (LTR, gag, env, pol, tax/rex) and against HTLV-II pol and gag. Reverse transcriptase (RT) activity was measured on supernatants from STCs using a sensitive PCR-based technique. No HTLV-I or -II sequences were found by PCR nor RT activity detected in the 64 cases. Our findings do not provide evidence of HTLV-I or -II infection in T-PLL and LGL leukemia patients from an HTLV-I nonendemic area. Previous positive reports on these disorders may represent technical artefacts, detection of endogenous HTLV-like sequences or reflect patients from endemic areas and a variable etiology of T cell diseases.
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PMID:The human T-cell lymphotropic viruses types I/II are not involved in T prolymphocytic leukemia and large granular lymphocytic leukemia. 926 85

Association between mycosis fungoides (MF), its leukaemic variant Sezary syndrome (SS) and the human T-cell lymphotropic virus type-I (HTLV-I) has been controversial, with the reported incidence of infection varying between 0% and nearly 100%. We studied 127 patients (85 MF, 28 SS, five Sezary cell leukaemia, four lymphomatoid papulosis, and five unspecified cutaneous T-cell lymphomas (CTCL)) originating from Europe (France, Spain, U.K., Portugal) or from U.S.A. (California) for the presence of HTLV-I infection markers. HTLV-I and -II serology were performed on 78 patients using standard immunological methods. Reverse transcriptase (RT) assay was also performed in 26 cases using an RT-PCR-based method of high sensitivity. Molecular analyses were performed on 215 DNA samples (121 from fresh PBMCs, 26 from PBMCs after short-term culture and 68 from skin lesions) by PCR amplification using HTLV-I and -II gag, pol, env, pX and LTR specific primers. Immunological tests were negative except for two sera which were indeterminate. PCR with all HTLV-I and -II primer pairs showed negative results in all 215 samples investigated. No RT activity was detected in short-term PBMC cultures of any of the 26 cases studied. The results of this large study from five different countries clearly indicate that MF and SS are not associated with HTLV-I infection.
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PMID:Mycosis fungoides and Sezary syndrome are not associated with HTLV-I infection: an international study. 1055 37

Spontaneously activated MDV is rarely included in MDV-transformed cells, while it may influence the results of transcriptional analysis. A population consisting of 10(3) MDV-transformed cells probably did not include spontaneously activated MDV, since the estimated frequency of MDV-transformed cells including activated MDV was below 0.01% according to limiting-dilution polymerase chain reaction (PCR) and the presence of the major early antigen pp38 in 6 transformed cell lines. Reverse transcriptase-PCR (RT-PCR) products corresponding to ICP27, pol, TK, US3, A41, gA, gB and UL50 genes were undetectable in 10(3) cells by Southern hybridization of the RT-PCR products. Transcripts of the VP16 and SORF2 genes were detected in the 10(3) cells of MSB-1, and the pp14 gene transcript was found in 10(3) cells of RPL-1 but not in 10(3) cells of HPRS-1, MOGA-2, MSB-1 or MTB-1. A transcript corresponding to the ICP4 sequence was detected as a 0.7 kbp RT-PCR product in 10(3) cells of these MDV cell lines but not in the retrovirus-transformed 1104B1 cell line. The transcript corresponding to the 0.7 kbp RT-PCR product suggested a splice by its size and sequence. Thus, transcriptional analysis of 10(3) MDV-transformed cells revealed that the transcript corresponding to the ICP4 sequence was a common transcript in latently infected MDV-transformed cells, while most of the genes did not transcribe in these cells.
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PMID:Transcriptional analysis of Marek's disease virus (MDV) genes in MDV-transformed lymphoblastoid cell lines without MDV-activated cells. 971 10

A human cell line constitutively expressing the HIV-1 gag and pol genes products was established. The cell line was established by stably transfecting 293 cells with a plasmid construct that expresses the HIV Gag and Pol and can confer the transfectants resistant to mycophenolic acid. Particles generated from transient expression of the plasmid construct were noninfectious when pseudotyped with HIV envelope or with amphotropic murine leukemia virus envelope proteins. However, virus-like Gag particles produced by the stable cell line were appropriately processed, exhibited a wild-type retrovirus particle density, and possessed significant reverse-transcriptase (RT) activities. Continuous passage of the cell line either in the presence or absence of mycophenolic acid had no major effects on the Gag processing efficiency, particle assembly, or RT activity release. It was also demonstrated that the proteolytic processing of the virus-like particles released from the cell line was inhibited by an HIV protease inhibitor, saquinavir. The establishment of a stable cell line producing noninfectious but proteolytically processed HIV Gag particles offers a safe, convenient tool for biochemical and immunological analysis of virus-like particle assembly and is very useful for the development of anti-HIV protease drugs.
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PMID:A human cell line constitutively expressing HIV-1 Gag and Gag-Pol gene products. 989 Apr 17

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

Reverse transcriptase (RT) isolated from Rous sarcoma virus (RSV) consists of heterodimeric RTalphabeta, RTalpha, and RTbeta. The alpha subunit (63 kDa) contains an N-terminal polymerase and a C-terminal RNase H domain. The N terminus of beta (95 kDa) corresponds to alpha with the integrase domain attached to the C terminus (32 kDa). We have constructed baculoviruses expressing the genes for alpha or beta or the entire pol (99 kDa). Infection of insect cells with recombinant virus yielded highly active and soluble RSV RT enzymes that could be purified to >90% homogeneity. HPLC gel filtration showed that alpha is a dimeric enzyme that can be partially monomerized upon the addition of 45% Me(2)SO. DNA synthesis on DNA-DNA and DNA-RNA primer-templates in the presence of competitor substrates revealed that alphabeta and beta as well as alpha are processive polymerases. However, the affinity of beta and alphabeta for primer-template substrates appears to be higher than that of alpha. All RSV enzymes investigated have the potential to displace RNA-RNA duplexes more efficiently than human immunodeficiency virus type 1 RT. Unlike human immunodeficiency virus type 1 RT, RSV RTs can catalyze an initial RNase H endonucleolytic cleavage of the RNA template but not a 3' --> 5' directed processing activity.
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PMID:Soluble Rous sarcoma virus reverse transcriptases alpha, alphabeta, and beta purified from insect cells are processive DNA polymerases that lack an RNase H 3' --> 5' directed processing activity. 1047 89

Reverse transcriptase (RT) preparations containing various molecular forms of the enzyme consisting of alpha- and/or beta-subunits have been isolated from E. coli cells transformed with plasmid pMF14 containing the Rous sarcoma virus (RSV) pol gene. The three possible dimeric forms of the enzyme demonstrated DNA polymerase activity, the relative activities of the alphaalpha, betabeta, and alphabeta forms being about 1:3:4. RNase H activity is associated with the betabeta and alphabeta dimers but not with the alphaalpha dimer. Comparison of the enzymic properties of the various dimers and dissociation--reassociation results suggest that the betabeta and alphabeta dimers of the RSV recombinant reverse transcriptase are similar to the corresponding virion RT forms.
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PMID:Isolation and characterization of Rous sarcoma virus recombinant reverse transcriptase dimers. 1049 11

Pigs are potential providers of donor tissues for xenotransplantation (e.g. of pancreatic islets) in Type 1 diabetes. In this context, our group has studied the use of islets from specific pathogen-free (SPF) pigs as a means of reducing the risks of "conventional zoonosis". Although this approach does not prevent the transmission of pig endogenous retrovirus (PERV) to humans, we attempted to determine the presence of C-type PERV mRNAs for gag, pol, and env subtypes as a first descriptive step in the retroviral characterisation of SPF pig tissues (especially pancreas). Using semiquantitative reverse-transcriptase polymer chain reaction with 18S rRNA and beta-actin as internal controls, PERV mRNA levels were compared in a large panel of tissues from SPF and conventional pigs. PERV mRNAs for gag, pol, env-A and env-B were present in all tissues studied from the nine SPF pigs tested. Signals for env-C mRNAs were of much lower intensity than those for env-A and B, and most often undetectable in pancreas. The mRNA levels for gag, pol, env-A, env-B and env-C mRNAs were lower in pancreas (p < 0.01) than in all other tissues. Among other porcine tissues likely to be grafted in man, the highest retroviral mRNA levels were detected in kidney (p < 0.01), followed by liver, lung and heart. Amplified PERV mRNA signals were about 17 times less frequent in pig pancreas than in the retroviral-producing porcine cell line G2, while kidney contained about 6 times more PERV mRNAs than pancreas. The levels of gag, pol, env-A, env-B, and env-C mRNAs also varied between tissues of conventional pigs: PERV mRNA levels were lowest in pancreas, and env-C mRNAs were most often undetectable. For all SPF tissues tested, pol, gag, env-A, env-B, and env-C mRNA levels were in the same range or slightly higher than in corresponding tissues of conventional pigs. In summary, this study of C-type PERV mRNAs in a large panel of tissues from SPF pigs, in the context of our strategy of quality assurance and sanitary control, indicated that PERV mRNA levels were in the same range in SPF and corresponding conventional pig tissues, confirming that the use of SPF pigs would not prevent the risk of PERV transmission to human recipients of xenografts. PERV-A and PERV-B may be mainly represented, and PERV-C much less, in these pig tissues (particularly pancreas). The fact that pancreas expressed the lowest PERV mRNA levels and kidney the highest, among porcine tissues likely to be grafted, could be of interest from a clinical point of view. Pig tissues may differ in their loads of PERV sequences, which could be a factor in the risk of PERV transmission during xenotransplantation.
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PMID:Porcine endogenous retroviral mRNAs in pancreas and a panel of tissues from specific pathogen-free pigs. 1063 79


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