Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.49 (reverse transcriptase)
 31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The nucleotide sequence of the human spumaretrovirus (HSRV) genome was determined. The 5' long terminal repeat region was analyzed by strong stop cDNA synthesis and S1 nuclease mapping. The length of the RU5 region was determined and found to be 346 nucleotides long. The 5' long terminal repeat is 1,123 base pairs long and is bound by an 18-base-pair primer-binding site complementary to the 3' end of mammalian lysine-1,2-specific tRNA. Open reading frames for gag and pol genes were identified. Surprisingly, the HSRV gag protein does not contain the cysteine motif of the nucleic acid-binding proteins found in and typical of all other retroviral gag proteins; instead the HSRV gag gene encodes a strongly basic protein reminiscent of those of hepatitis B virus and retrotransposons. The carboxy-terminal part of the HSRV gag gene products encodes a protease domain. The pol gene overlaps the gag gene and is postulated to be synthesized as a gag/pol precursor via translational frameshifting analogous to that of Rous sarcoma virus, with 7 nucleotides immediately upstream of the termination codons of gag conserved between the two viral genomes. The HSRV pol gene is 2,730 nucleotides long, and its deduced protein sequence is readily subdivided into three well-conserved domains, the reverse transcriptase, the RNase H, and the integrase. Although the degree of homology of the HSRV reverse transcriptase domain is highest to that of murine leukemia virus, the HSRV genomic organization is more similar to that of human and simian immunodeficiency viruses. The data justify classifying the spumaretroviruses as a third subfamily of Retroviridae.
 ...
PMID:Analysis of the primary structure of the long terminal repeat and the gag and pol genes of the human spumaretrovirus. 245 55

The DNA sequence of the gag and pol regions of a provirus cloned from a bovine tumor is presented. In order to confirm these results the sequence of portions of a second clone, derived from a virus-producing cell line, was also determined. The gag gene was found to consist of 1179 nucleotides, which probably encode only three proteins: an N-terminal protein of 109 amino acids, a major core protein (p24) of 215 amino acids, and a nucleic acid binding protein (p12) of 69 residues. An open reading frame, whose translated product showed clear homology to the avian and murine proteases, was found beginning immediately upstream of the 3' end of gag. Following this protease region, a third long open reading frame, encoding 852 amino acids, showed clear homology to both avian and murine pol genes. The mechanism of translation of the protease and pol gene products cannot be predicted with certainty. Like Moloney murine leukemia virus (M-MuLV), BLV has a termination signal at the 3' end of gag, but unlike M-MuLV the protease is in a different reading frame. Like Rous sarcoma virus (RSV), BLV has a termination signal at the 3' end of the protease region and the reverse transcriptase is in a different (i.e., the third) reading frame. Possible translation mechanisms are discussed. Finally, the BLV gag and pol gene products are highly related to those of the human T-cell leukemia virus (HTLV); relatedness varied from 37% amino acid identities within the N terminal gag protein to 54% within the nucleic acid binding protein. Highly significant homology with both murine and avian type-C proteins was found within p24, p12, and the putative protease, reverse transcriptase, and endonuclease. Based on this homology, the BLV-HTLV family of viruses appears about equally distantly related to murine and avian type-C viruses.
 ...
PMID:The gag and pol genes of bovine leukemia virus: nucleotide sequence and analysis. 299 90

A murine monoclonal antibody (MAb), named C.V.K., was produced after immunization with highly purified and sonicated lymphadenopathy-associated virus (LAV). No monoclonal antibody was observed with intact virus used as immunogen. C.V.K. MAb recognizes an epitope present on the precursor gag protein of 55 kilodaltons. Western blot analysis and pulse-chase experiments support the interpretation that after p55 cleavage into p25, p18, and p13, only p18 expresses this epitope. C.V.K. MAb selectively stained only LAV-infected lymphocytes. This intracytoplasmic staining appears 3 days after the infection and is correlated with reverse transcriptase activity. Neither membrane immunofluorescence of infected lymphocytes nor neutralizing activity was observed with C.V.K. MAb. These facts suggest that p55 and p18 are not expressed at the cell membrane or on the viral envelope. C.V.K. MAb should prove useful not only in the purification of core proteins but also for detecting infected cells producing the virus in suspension or on histologic sections.
 ...
PMID:A monoclonal antibody against LAV gag precursor: use for viral protein analysis and antigenic expression in infected cells. 300 97

The analysis of retroviral mutants has played a critical role in the development of our understanding of the complex viral life cycle. The most fundamental result of that analysis has been the definition of the replication functions encoded by the viruses. From a biochemical examination of a particular step in the life cycle it is difficult to determine, for example, whether that step is catalyzed by a viral or a host enzyme; but the isolation of a viral mutant defective in that step can firmly establish that a viral function is involved. In this way many facts about the viruses have been established. We know that reverse transcriptase is encoded by the virus; that RNAase H and DNA polymerase activities reside on the same gene product; that processing of many precursor proteins is mediated by a viral proteinase; and that establishment of the integrated provirus requires a viral protein. The list of functions mediated by viral enzymes has largely been defined by the mutants isolated and studied in various laboratories. The second significant result of the studies of viral mutants has been the assignation of the replication functions to particular viral genes, and then more specifically to particular domains of these genes. Mutants and viral variants have been essential in the determination, for example, that the gag protein is the critical gene product for the assembly of a virion particle; that the env protein is the determinant of species specificity of infection; or that the LTR is a major determinant of tissue tropism and leukemogenicity. The subdivisions of functions within a given gene have similarly hinged on mutants. Genetic mapping was needed to establish that P30 is the most important region for assembly; that the proteinase and integrase functions reside, respectively, in the 5' and 3' portions of the pol gene; and that the glycosylated gag protein is dispensable for replication. A third important area of knowledge has depended heavily on viral mutants: the determination of host functions and proteins that interact with viral proteins. Variant viruses with altered or restricted host ranges serve to define differences between pairs of different host cells, and the mapping of the viral mutations serves to define the viral protein important in that interaction with the host. These studies are only in their infancy, but it is clear that substantial efforts will be made to further analyze these host functions.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:Mutants of murine leukemia viruses and retroviral replication. 303 30

Two revertants of ts110 Moloney murine sarcoma virus (MuSV) with wild-type MuSV phenotype were examined for the presence of mos gene products, ts110 MuSV has a temperature-sensitive defect in a function required to maintain the transformed phenotype. The nonproducer 6m2 cell clone transformed by ts110 produces an 85,000-Da gag-mos protein (P85gag-mos) and a 58,000-Da gag protein (P58gag). A spontaneous revertant (clone 54-5A4) of the 6m2 cell clone produces a 100,000-Da protein (P100) recognized by antisera raised against murine leukemia virus p15, p12, and p30 but lacks determinants of p10, reverse transcriptase, and gp70. P100 was specifically recognized by antisera (anti-C3) prepared against a synthetic peptide representing the predicted C-terminal 12 amino acids of Moloney MuSV v-mos gene. Normal sera or anti-C3 blocked with excess synthetic peptide did not recognize P100. Thus, P100 is a product of the gag and mos genes. P100 was found to be phosphorylated. A second wild-type revertant (clone 204-3) was obtained by superinfection of ts110 nonproducer cells with Simian sarcoma associated virus (SSAV); it was also found to contain a phosphorylated P100gag-mos protein. The 204-3 cell clone also contained two gag polyproteins (Pr60gag and Pr55gag) of the size and antigenic properties of those found in SSAV-infected cells. These results provide two examples of P100 gag-mos proteins both derived from the P85gag-mos producing 6m2 cell clone. The P100 gag-mos polyproteins are made in amounts that are easily detected by radiolabeling experiments using [3H]leucine. The intracellular viral RNAs present in 6m2 cells and the two revertant clones were also examined. All three cell clones contained a 4.0 kb RNA hybridizing to v-mos sequences but only the 6m2 clone contained a 3.5 kb mos-containing RNA. Our findings indicate that the 3.5 kb RNA codes for P85gag-mos in cell-free translation experiments (Junghans et al., 1982, J. Mol. Biol. 161, 229). These findings as they relate to the mechanism that produces P100gag-mos instead of P85gag-mos are discussed.
 ...
PMID:Gag-mos Polyproteins encoded by variants of the Moloney strain of mouse sarcoma virus. 630 90

Human chorionic gonadotropin (hCG)--a pregnancy-associated immunomodulating hormone--has been recently shown in vitro to suppress reverse transcriptase activity in chronically HIV-infected lymphocytes and monocytes and to block viral transmission resulting from cell-cell contact between virus-carrying lymphocytes and placental trophoblasts. In further pursuit of the query into the mechanism of action, purified alpha and beta subunits of hCG were tested for the inhibition of p24 gag protein synthesis in virus-producing ACH-2 lymphocytes and U1 monocytes. Unlike the alpha subunit, beta-hCG displayed a distinct U-shaped dose response, characteristic of the effect of dimer hCG. Maximum inhibition of viral expression has been achieved at 10-100 ng/ml, the concentration corresponding to blood levels of beta-hCG in pregnant women. The doses that were several logs higher of normal levels seemed to increase viral production in monocytes. The data presented supports our original observations regarding the effect of intact hCG on HIV replication. While the mechanism of action remains to be established, the results suggest that the virus-interfering activity of hCG is determined by hormone-specific beta chain but not by the alpha subunit--shared with the family of glycoprotein hormones from the pituitary--follicle-stimulating hormone, luteinizing hormone and thyrotropin.
 ...
PMID:Anti-HIV effect of beta subunit of human chorionic gonadotropin (beta hCG) in vitro. 753 8

We generated monoclonal antibodies (MAB) against feline immunodeficiency virus (FIV) and characterized these MAB by single competition enzyme immunoassays (EIA), immunoblot analysis, and radioimmunoprecipitation. Four MAB identified 3 distinct epitopes of the FIV p24/26 gag major core protein. One MAB recognized the p16/17 gag protein; none recognized envelope proteins. We developed an FIV p26 antigen capture EIA that proved more sensitive (0.5 ng of p26/ml), less expensive, and less time-consuming than reverse transcriptase assay. The same MAB were used to develop an antibody EIA specific for FIV p26. The MAB and capture assays reported should prove useful in FIV diagnosis and research.
 ...
PMID:Development of monoclonal antibodies and capture immunoassays for feline immunodeficiency virus. 754 55

The role of the RNA secondary structure in the 5' packaging signal region of human immunodeficiency virus type 1 (HIV-1) in initiating translation of gag mRNA has been investigated both in vitro and in the presence of cellular cofactors in vivo. Heat denaturation of the structure and mutagenic deletion both lead to an increase in levels of translated products, indicating that the structure is a significant inhibitor of translation. The proximity of the gag AUG to the packaging signal structure suggested that it might function as an internal ribosome entry site. However, in both a cell-free system and eukaryotic cells, translation will initiate at a novel upstream initiation codon introduced within the 5' noncoding region. This codon is utilized exclusively, resulting in gag protein products with an extra 11 amino acids at the amino terminus, which, when expressed in T lymphocytes, are confined intracellularly, probably because of the lack of an N-terminal glycine myristoylation signal. Deletion of the secondary structure abolishes gag production even in the presence of tat and rev in trans. Using dicistronic constructs containing the HIV-1 5' leader cloned between two heterologous open reading frames, we were unable to detect any significant expression of the second open reading frame that would have been supportive of an internal ribosome entry site mechanism. Using mutant proviruses either lacking the entire packaging signal structure region or containing the introduced upstream initiation codon in long-term replication studies, we were unable to detect reverse transcriptase activity in culture supernatants. The 5' packaging signal structure of HIV-1 does not serve as an internal ribosome entry site. The translation of gag is consistent with ribosomal scanning. However, the packaging signal structure causes significant translational inhibition.
 ...
PMID:The human immunodeficiency virus type 1 5' packaging signal structure affects translation but does not function as an internal ribosome entry site structure. 855 34

A major component of Drosophila telomeres is the retrotransposon HeT-A, which is clearly related to other retrotransposons and retroviruses. This retrotransposon is distinguished by its exclusively telomeric location, and by the fact that, unlike other retrotransposons, it does not encode its own reverse transcriptase. HeT-A coding sequences diverge significantly, even between elements within the same genome. Such rapid divergence has been noted previously in studies of gag genes from other retroelements. Sequence comparisons indicate that the entire HeT-A coding region codes for gag protein, with regions of similarity to other insect retrotransposon gag proteins found throughout the open reading frame (ORF). Similarity is most striking in the zinc knuckle region, a region characteristic of gag genes of most replication-competent retroelements. We identify a subgroup of insect non-LTR retrotransposons with three zinc knuckles of the form: (1) CX2CX4HX4C, (2) CX2CX3HX4C, (3) CX2CX3HX6C. The first and third knuckles are invariant, but the second shows some differences between members of this subgroup. This subgroup includes HeT-A and a second Drosophila telomeric retrotransposon, TART. Unlike other gag regions, HeT-A requires a -1 frameshift for complete translation. Such frameshifts are common between the gag and pol sequences of retroviruses but have not before been seen within a gag sequence. The frameshift allows HeT-A to encode two polypeptides; this mechanism may substitute for the post-translational cleavage that creates multiple gag polypeptides in retroviruses. D. melanogaster HeT-A coding sequences have a polymorphic region with insertions/deletions of 1-31 codons and many nucleotide changes. None of these changes interrupt the open reading frame, arguing that only elements with translatable ORFs can be incorporated into the chromosomes. Perhaps HeT-A translation products act in cis to target the RNA to chromosome ends.
 ...
PMID:The gag coding region of the Drosophila telomeric retrotransposon, HeT-A, has an internal frame shift and a length polymorphic region. 899 54

Retrovirally encoded proteases are responsible for the maturation of immature viral particles yielding mature, infectious virus. This is done by apparent (auto)-processing and self-activation of the protease (PR) from a larger viral gag-PR-(pol) protein (zymogen) precursor and subsequent processing of the viral reverse transcriptase (RT) and integrase (IN), and the gag protein precursor into mature gag proteins. Only the matured components are capable of forming capsids for intact, infectious viruses. Blocking this proteolytic process results in production of immature, non-infective virions. All retroviral proteases are aspartic-type proteases. Determination of the three-dimensional structure revealed retroviral proteases as small, nearly symmetric homodimers. This prompted de novo design of inhibitors for the HIV protease taking advantage of the unique symmetric structure of the active center, unparalleled by cellular proteases. The novel substances inhibit in vitro the HIV protease at nanomolar/subnanomolar concentrations and exhibit very low toxicity. They are inactive against human proteases such as renin or pepsin. The HIV protease inhibitors (PI) represent a promising alternative to the reverse transcriptase (RT) inhibitors (AZT, ddC, ddI) hitherto used with limited success for HIV chemotherapy. Clinical studies confirmed the low toxicity but revealed a pharmacological pattern typical for these hydrophobic compounds, such as low water solubility, poor oral bioavailibility, and short plasma half-life. Typical for antimicrobial agents, also a resistance phenomenon became evident. Latest clinical results show, however, promisingly that both problems might be overcome by application of the PI in combination with RT inhibitors (such as AZT, ddI or ddC) exerting a remarkable synergistic antiviral effect with lasting restoration of the CD4-T-cell level.
 ...
PMID:Retroviral proteases: structure, function and inhibition from a non-anticipated viral enzyme to the target of a most promising HIV therapy. 899 87


<< Previous 1 2 3 Next >>