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:2.7.7.49 (reverse transcriptase)
31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ty3 is a Saccharomyces cerevisiae retrotransposon that integrates near the transcription initiation sites of polymerase III-transcribed genes. It is distinct from the copialike Ty1 and Ty2 retrotransposons of S. cerevisiae in both the sequences of encoded proteins and gene order. It is a member of the gypsylike family of retrotransposons which resemble animal retroviruses. This study was undertaken to investigate the nucleocapsid particle of a transpositionally active gypsylike retrotransposon. Characterization of extracts from cells in which Ty3 expression was induced showed the presence of Ty3 nucleoprotein complexes, or viruslike particles, that migrated on linear sucrose gradients with a size of 156S. These particles are composed of Ty3 RNA, full-length, linear DNA, and proteins. In this study, antibodies raised against peptides predicted from the Ty3 sequence were used to identify Ty3-encoded proteins. These include the capsid (26 kDa), nucleocapsid (9 kDa), and reverse transcriptase (55 kDa) proteins. Ty3 integrase proteins of 61 and 58 kDa were identified previously (L. J. Hansen and S. B. Sandmeyer, J. Virol. 64:2599-2607, 1990). Reverse transcriptase activity associated with the particles was measured by using exogenous and endogenous primer-templates. Immunofluorescence studies of cells overexpressing Ty3 revealed cytoplasmic clusters of immunoreactive proteins. Transmission electron microscopy showed that Ty3 viruslike particles are about 50 nm in diameter. Thus, despite the unusual position specificity of Ty3 upstream of tRNA-coding regions, aspects of the Ty3 life cycle are fundamentally similar to those of retroviruses.
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PMID:Ty3 GAG3 and POL3 genes encode the components of intracellular particles. 137 Nov 65

A retrotransposon from the fungal tomato pathogen Cladosporium fulvum (syn. Fulvia fulva) has been isolated and characterised. It is 6968 bp in length and bounded by identical long terminal repeats of 427 bp; 5 bp target-site duplications were found. Putative first- and second-strand primer binding sites were identified. Three long open reading frames (ORFs) are predicted from the sequence. The first has homology to retroviral gag genes. The second includes sequences homologous to protease, reverse transcriptase, RNAse H and integrase, in that order. Sequence comparisons of the predicted ORFs indicate that this element is closely related to the gypsy class of LTR retrotransposons. Races of the pathogen exhibit polymorphisms in their complement of at least 25 copies of the sequence. Virus-like particles which co-sediment with reverse transcriptase activity were observed in homogenates of the fungus. This is the first report of an LTR retrotransposon in a filamentous fungus.
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PMID:CfT-I: an LTR-retrotransposon in Cladosporium fulvum, a fungal pathogen of tomato. 137 73

The expression of the pol gene of human immunodeficiency virus type 1 occurs via a ribosomal frameshift between the gag and pol genes. The resulting protein, a Gag-Pol polyprotein, is produced at a level 5 to 10% of that of the Gag protein. The Gag-Pol polyprotein is incorporated into virions and provides viral protease, reverse transcriptase, and integrase, which are essential for infectivity. It is generally believed that the Gag-Pol polyprotein is incorporated into virions via interaction with the Gag protein, although the details of the mechanism are unknown. To further study this problem, we have constructed a human immunodeficiency virus type 1 proviral genome which overexpresses the Gag-Pol polyprotein (Pr160gag-pol). Transfection of this proviral genome (pGPpr-) into COS-1 cells resulted in the expression of full-length Pr160gag-pol polyprotein. Although the majority of the Pr160gag-pol was confined to the cells, low levels of reverse transcriptase activity were detectable in the cell supernatants. The cotransfection of pGPpr- with a second plasmid which expresses only the Pr55gag precursor (pGAG) resulted in a significantly higher level of Pr160gag-pol in the medium of transfected cells. Sedimentation analysis using sucrose density gradients demonstrated that most Pr160gag-pol was found in fractions corresponding to the density of virion particles, indicating that the Pr160gag-pol polyprotein was released in association with a Pr55gag viruslike particle. To further characterize the requirements for the release, a mutation was constructed to express an unmyristylated Pr160gag-pol polyprotein. Coexpression with Pr55gag demonstrated that the unmyristylated Pr160gag-pol was also incorporated into virion particles. Subcellular fractionation experiments revealed that the distributions of the Pr160gag-polmyr- and Pr160gag-pol in the membrane and cytosol were similar under low- or high-ionic-strength conditions. Taken together, these results suggest that myristylation of the Pr160gag-pol polyprotein is not required for the interaction with the Pr55gag necessary for packaging into a viruslike particle.
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PMID:The nonmyristylated Pr160gag-pol polyprotein of human immunodeficiency virus type 1 interacts with Pr55gag and is incorporated into viruslike particles. 138 61

Human immunodeficiency virus (HIV) has been implicated as the etiologic agent of acquired immunodeficiency syndrome and is a member of the sub-family Lentivirinae within the family Retroviridae. HIV type 1 (HIV-1) contains three major genes, gag, pol and env, which code for (1) core proteins, (2) a protease, reverse transcriptase and integrase, and (3) envelope glycoproteins, respectively. The core proteins p17, p24 and p15 are derived from gag precursor, p55, by endoproteolytic cleavage. The two nucleic-acid-binding proteins p7 and p9 are synthesized from p15 by proteolytic cleavage. These two structural proteins are apparently needed for the ribonucleoprotein-core formation. The envelope glycoproteins gp120 and gp41 (gp120-gp41 complex) are also generated by cleavage env precursors, gp160. The assembly of HIV-1 particles, like other retroviruses, appears to involve the association of the env precursor gp160 with the gag proteins. There are several factors which influence the assembly and budding process of HIV-1. In this article, we describe important events in HIV-1 morphogenesis and factors which influence this aspect of the HIV-1 life cycle.
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PMID:Morphogenesis of human immunodeficiency virus type 1. 138 14

Human immunodeficiency virus type 1 (HIV-1) integrase (IN) is the viral protein required for integration of the HIV-1 genome into host cell DNA. A series of clones expressing portions of IN as lambda cII fusion proteins has been constructed in an Escherichia coli expression system; a Southwestern procedure was used to examine binding of the expressed proteins to DNA oligonucleotides. Proteins expressed by clone pHIP106, encoding the entire IN protein but no other pol sequence, and pKNA101, which expresses an IN fusion protein containing 23 amino acids of HIV-1 reverse transcriptase at its amino terminus, exhibited similar levels of oligonucleotide binding. Little DNA sequence specificity was associated with binding activity and there was a preference for Mn2+ over Mg2+ and Ca2+. Interestingly, the protein expressed by an N-terminal clone containing nucleotides coding for IN amino acids 1-141 (including a conserved His-Cys box) was unable to bind oligonucleotide, whereas the protein expressed by a C-terminal clone containing nucleotides coding for amino acids 142-288 exhibited binding equivalent to that of full-length IN. The C-terminal protein was unreactive with a MAb to the lambda cII leader peptide and with an antipeptide serum directed against amino acids 141-158. These results are consistent with the previously reported internal initiation of IN protein synthesis in E. coli at met 154, and indicate that the C-terminal clone does not express IN amino acids 142-153. These amino acids represent part of a conserved region termed D(35)E, containing amino acids 116-152, which has been implicated in IN DNA binding.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Localization of DNA binding activity of HIV-1 integrase to the C-terminal half of the protein. 154 Apr 16

The retroid family consists of all genetic elements that encode a potential reverse transcriptase (RT). Members of this family include a diversity of eukaryotic genetic elements (viruses, transposable elements, organelle introns, and plasmids) and the retrons of prokaryotes. Some retroid elements have, in addition to the RT gene, other genes in common with the retroviruses. On the basis of RT sequence similarity, the retroposon group is defined as the eukaryotic long interspersed nuclear elements, the transposable elements of (1) Drosophila melanogaster (I and F factors), (2) Trypanosoma brucei (ingi element), (3) Zea mays (Cin4), (4) Bombyx mori (R2Bm), and members of the group II introns and plasmids of yeast mitochondria. The data presented here elucidate the extent of the relationships between the retroposons and other retroid-family members. Protein-sequence alignment data demonstrate that subsets of the retroposons contain different assortments of retroviral-like genes. Sequence similarities can be detected between the capsid, protease, ribonuclease H, and integrase proteins of retroviruses and several retroposon sequences. The relationships among the retroposon capsid-like sequences are congruent with the RT sequence phylogeny. In contrast, the similarity between ribonuclease H sequences varies in different subbranches of the retroposon lineage. These data suggest that xenologous recombination (i.e., the replacement of a homologous resident gene by a homologous foreign gene) and/or independent gene assortment have played a role in the evolution of the retroposons.
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PMID:Evolution of retroposons by acquisition or deletion of retrovirus-like genes. 166 70

Approximately 50% of the ribosomal DNA (rDNA) units of Drosophila melanogaster are inactivated by two different 28 S RNA ribosomal gene insertions (type I and type II). We present here the nucleotide sequence of complete type I and type II elements. Conceptual translation of these sequences revealed open reading frames (ORFs) encoding amino acid residues conserved in all retrotransposable elements. Full-length type I elements are 5.35 x 10(3) base-pairs in length and contain two overlapping ORFs. The smaller ORF (471 amino acid residues) has similarity to gag genes, while the larger ORF (1021 residues) has similarity to pol genes. Full-length type II elements are 3.6 x 10(3) base-pairs and contain one large ORF (1056 residues) that appears to represent a gag-pol fusion. Type I and type II elements are similar in structure, in the proteins they encode, and in insertion specificity to the R1Bm and R2Bm retrotransposable elements of Bombyx mori. We suggest that the D. melanogaster elements be called R1Dm and R2Dm, to reflect their structure as retrotransposons. Comparison of the R1 and R2 elements from these two widely different species revealed regions of the ORF that are likely to play an important role in the propagation of the elements. Four distinct regions of sequence conservation separated by regions of little or no sequence similarity were detected for both the R1 and R2 elements: (1) cysteine motifs of the gag gene, with three such motifs for R1 and one motif for R2; (2) a reverse transcriptase domain; (3) an integrase domain located carboxyl terminal to the reverse transcriptase region; and (4) a small region amino terminal to the reverse transcriptase domain, whose function is not known. The level of identity of the amino acid residues for these segments is 28 to 34% between the R1 elements, and 34 to 39% for the R2 elements. Finally, it may be predicted that the mechanism of unequal crossover might eventually eliminate R1 and R2 from the rDNA locus. The long history of selection at the protein level exhibited by these elements indicates that it is their active transposition that maintains them in the locus. The high level of sequence homogeneity between copies of each element within the same species is consistent with the high turnover rate expected to result from these processes.
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PMID:Type I (R1) and type II (R2) ribosomal DNA insertions of Drosophila melanogaster are retrotransposable elements closely related to those of Bombyx mori. 169 Aug 12

The Mauriceville and Varkud mitochondrial plasmids of Neurospora are closely related, closed-circular DNAs (3.6 and 3.7 kilobases, respectively) that have characteristics of mtDNA introns and retroid elements. The plasmids contain a single long open reading frame (710 amino acids), whose amino-terminal half has structural similarity to reverse transcriptases. Using antibodies against synthetic peptides and trpE fusion proteins, we detected an 81-kDa protein encoded by this open reading frame in mitochondrial preparations from the plasmid-containing strains. This 81-kDa protein cosegregates with reverse transcriptase activity in sexual crosses and comigrates with reverse transcriptase activity in sodium dodecyl sulfate-polyacrylamide gels, where it can be assayed after renaturation of the protein. In glycerol gradients under nondenaturing conditions, the reverse transcriptase activity sediments at approximately 145 kDa, close to the value expected for a dimer of the 81-kDa protein. The 81-kDa protein represents most of the 710-amino acid open reading frame, but may be missing some amino acids at the amino terminus. The regions upstream and downstream of the putative reverse transcriptase domain lack sequences characteristic of gag, protease, RNase H, or integrase domains found in other retroid elements. The plasmid-encoded 81-kDa protein seems to be a novel type of reverse transcriptase that may provide insight into the evolution of these enzymes.
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PMID:Identification of the reverse transcriptase encoded by the Mauriceville and Varkud mitochondrial plasmids of Neurospora. 169 Nov 79

As human immunodeficiency virus type 1 (HIV-1) has become better understood, numerous drugs have been developed that act at virus-specific sites. These are challenging our ability to evaluate them thoroughly and rapidly. Zidovudine (AZT) remains the mainstay of anti-HIV-1 drugs. Recent controlled trials indicate it should be used early in infection (in those with CD4 cell counts less than 500/mm3) and in lower doses (500-600 mg/day). Prolonged AZT treatment in patients with AIDS, however, is often associated with viral resistance. Newer reverse transcriptase-inhibiting nucleoside derivatives are currently in phase II-III clinical trials. Other HIV-1 replicative sites under attack in clinical studies include binding and entry of virus, envelope protein glycosylation, and viral assembly and release. Agents that target HIV-1 proteinase, integrase, ribonuclease H, and products of regulatory genes such as tat are under development. Combination therapies that target different viral replicative sites likely will allow use of individual agents below their toxic concentrations and help prevent drug resistance. Innovative programs for expanded access to experimental drugs are needed that will permit expeditious clinical trials, optimize the gathering of useful information, and permit the widest access to promising treatments.
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PMID:Chemotherapy of human immunodeficiency virus infections: current practice and future prospects. 169 Dec 43

A single copy of the retrotransposon TED, from the moth Trichoplusia ni (a lepidopteran noctuid), was identified within the DNA genome of the baculovirus Autographa californica nuclear polyhedrosis virus. Determination of the complete nucleotide sequence (7,510 base pairs) of the integrated copy indicated that TED belongs to the family of retrotransposons that includes Drosophila melanogaster elements 17.6 and gypsy and thus represents the first nondipteran member of this invertebrate group to be identified. The internal portion of TED, flanked by long terminal repeats (LTRs), is composed of three long open reading frames comparable in size and location to the gag, pol, and env genes of the vertebrate retroviruses. Sequence similarity with the dipteran elements was the highest within individual domains of TED open reading frame 2 (pol region) that are also conserved among the retroviruses and encode protease, reverse transcriptase, and integrase functions, respectively. Mapping the 5' and 3' termini of TED RNAs indicated that the LTRs have a retroviral U3-R-U5 structural organization that is capable of directing the synthesis of transcripts that represent potential substrates for reverse transcription and intermediates in transposition. Abundant RNAs were also initiated from a site within the 5' LTR that matches the consensus motif for the promoter of late, hyperexpressed baculovirus genes. The presence of this viruslike promoter within TED and its subsequent activation only after integration within the viral genome suggest a possible symbiotic relationship with the baculovirus that could extend transposon host range.
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PMID:Gene organization and transcription of TED, a lepidopteran retrotransposon integrated within the baculovirus genome. 169 64


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