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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)

A hybrid dysgenesis syndrome similar to those described in Drosophila melanogaster occurs in Drosophila virilis when a laboratory stock is crossed to a wild strain collected in the Batumi region of Georgia (U.S.S.R). Mutations in various loci obtained during these crosses are presumably induced by the insertion of DNA sequences. We have cloned an induced white mutation and characterized the insertion sequence responsible for the mutant phenotype. This sequence is a 10.6-kilobase (kb) transposable element we have named Ulysses. This element is flanked by unusually large 2.1-kb long terminal repeats. Ulysses also contains other landmarks characteristic of the retrotransposon family, such as a tRNA-binding site adjacent to the 5' long terminal repeat and open reading frames encoding putative products with homology to the reverse transcriptase, protease, and integrase domains typical of proteins encoded by vertebrate retroviruses. Some of the mutations obtained do not contain a copy of the Ulysses element at the mutant locus, suggesting that a different transposable element may be responsible for the mutation. Therefore, Ulysses may not be the primary cause of the entire dysgenic syndrome, and its mobilization may be the result of activation by an independent mobile element.
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PMID:A long terminal repeat-containing retrotransposon is mobilized during hybrid dysgenesis in Drosophila virilis. 217 8

We have determined the complete 9202 nucleotide sequence of the visna lentivirus. The deduced genetic organization most closely resembles that of the AIDS retrovirus in that there is a novel central region separating pol and env. Moreover, there is a close phylogenetic relationship between the conserved reverse transcriptase and endonuclease/integrase domains of the visna and AIDS viruses. These findings support the inclusion of the AIDS virus in the retroviral subfamily Lentivirinae.
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PMID:Nucleotide sequence of the visna lentivirus: relationship to the AIDS virus. 241 Jan 40

The nucleotide sequence of the internal region of a Drosophila retrotransposon. 412, was determined. The genome of 412 was found to consist of two long open-reading frames (ORFs 1 and 2), an unusually long putative leader region and long terminal repeats (LTRs). As with 17.6, 297 and gypsy, ORFs 1 and 2 slightly overlap each other and are out of phase by +2. ORF2 includes the nucleotide sequences coding for the putative protease, reverse transcriptase and integrase, and is similar in entire organization to the pol gene of Moloney murine leukaemia virus. In spite of the difference in insertion specificity, integrase, an enzyme presumably responsible for insertion, was found to be similar in amino acid sequence to the counterparts of 17.6, 297 and gypsy. There is no ORF in 412 which corresponds to retroviral env or ORF3s of 17.6 and 297. Analysis of 412 transcripts suggested that 412 LTR is composed of U3, R and U5. The gene for a potential primer tRNA for putative reverse transcription of 412 was also surveyed and the 3'-terminal 15 nucleotides of a putative arginine tRNA were found to be exactly complementary to the putative primer-binding site of 412.
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PMID:Nucleotide sequence characterization of a Drosophila retrotransposon, 412. 242 8

A mechanism to explain somatic hypermutation in immunoglobulin variable region genes is proposed employing polynucleotide information transfer through the error prone DNA----RNA----DNA loop. During transcription of the rearranged V-region, the primary transcript undergoes either inappropriate termination, cleavage, or reverse transcriptase priming allowing a V-region specific reverse-transcriptase-integrase complex to synthesize a DNA copy of the rearranged V-region and integrate it, by homologous recombination, back into the normal chromosomal site. Some consequences and predictions of the hypothesis are discussed.
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PMID:Hypothesis: somatic hypermutation by gene conversion via the error prone DNA----RNA----DNA information loop. 244 41

A category of viruses has been identified which is related to human immunodeficiency virus (HIV) but is more closely related to a group of simian retroviruses (STLV-III). These viruses named HTLV-IV, LAV-II, or SBL-6669, are prevalent in West-Africa. In this study, we analysed the cross-reactivity at the protein level between HTLV-IV and HIV (HTLV-IIIB). The results indicate that most people infected with HTLV-IV have antibodies that react to the major gag protein of HIV p 24. There is also a high degree of immunologic cross-reactivity between the pol gene products of HIV and HTLV-IV. Among these the endonuclease/integrase is more conserved than the reverse transcriptase. In contrast, the envelope glycoproteins that are the most frequently detected antigens by antibodies from exposed individuals are serotype specific. These data make the env gene products the most interesting antigens for serotype specific diagnosis of human retroviruses infections.
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PMID:A STLV-III related human retrovirus, HTLV-IV: analysis of cross-reactivity with the human immunodeficiency virus (HIV). 244 14

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.
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PMID:Analysis of the primary structure of the long terminal repeat and the gag and pol genes of the human spumaretrovirus. 245 55

Previous work indicates that hepatitis B virus (HBV) and retroviruses utilize a unique mechanism for genome replication by reverse transcription of RNA and share homology in biologically important nucleotide and protein sequences. The data presented here extend previous findings of sequence homology among the genomes of the members of these virus families. HBV was found to possess sequences homologous to the retrovirus protease and reverse transcriptase gene sequences. Homology was not found to the retrovirus integrase sequence consistent with the observation that hepadnaviruses do not integrate into cellular DNA as a necessary step in their replication cycle. Overall, the homology of the hepadnavirus polymerase gene was strongest with that of the murine leukemia viruses (MLVs). Also, the hepadnavirus polymerase shares organizational similarities to the MLV polymerase sequence. Analysis suggests that the ancestor of both hepadnaviruses and retroviruses possessed an overlapping long open reading frame in the polymerase gene sequence. In addition, low stringency blot hybridization using hepadnavirus DNA probes indicates that HBV is more closely related to MLV sequences than the sequences of MLV-related viruses and endogenous retrovirus-like genetic elements. Taken together, the data indicate that the polymerase gene sequence of the hepadnavirus and MLV genomes are organized in a similar fashion which suggests that these viruses evolved from a common ancestor.
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PMID:Close evolutionary relatedness of the hepatitis B virus and murine leukemia virus polymerase gene sequences. 245 12

The retrotransposon micropia was first described from Y-chromosomal fertility genes of Drosophila hydei. Screening a Drosophila melanogaster genomic library yielded several clones representing micropia elements in D. melanogaster. The DNA sequences of two elements from D. hydei (micropia-DhMiF2 and micropia-DhMiF8) and two elements from D. melanogaster (micropia-Dm2 and micropia-Dm11) permitted a detailed analysis of the spatial organization of micropia constituents. Micropia represents the typical gene organization represented by "core"-protein domains followed by a protease, reverse transcriptase, RNase and integrase domain. New features of the micropia family compared with other retrotransposons are: (1) a region of similarity to class I major histocompatibility complex antigens of mammals; (2) only one main open reading frame of about 4000 bases length; (3) a non-protein-coding region of about 500 base-pairs length between the 3' end of the open reading frame and the 5' start of the 3' long terminal repeat. This region includes 32 base-pair tandem repeats; (4) within the long terminal repeats, 82 base-pair tandem repeats with four potential ecdysteroid receptor binding sites. Because micropia combines many evolutionary features of different viruses, non-viral transposable elements, chromosomal genes and repetitive sequence organizations, this retrotransposon may be seen as a "minigenome" reflecting evolutionary principles of the construction of genomic components.
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PMID:Micropia: a retrotransposon of Drosophila combining structural features of DNA viruses, retroviruses and non-viral transposable elements. 246 89

Molecular evolution and phylogeny of different human immunodeficiency virus type 1 (HIV1) strains, of a type 2 (HIV2) strain, and of two simian immunodeficiency viruses (SIVAGM and SIVMAC) have been studied by comparing the nucleotide sequences of the two regions of their pol genes which encode the reverse transcriptase (RT) and endonuclease/integrase (EN). The analyses show that the different HIV 1s form one cluster (HIV1 group) and that the SIVs and HIV2 form another (HIV2 group). When the entire genomes of a HIV1, a HIV2, and the two SIVs were compared, the SIVAGM showed a unique pattern of mutation accumulations; that is, the SIVAGM has accumulated more nonsynonymous changes than synonymous changes in the RT and EN regions after its recent divergence from SIVMAC-142, and, furthermore, it has a deletion of approximately 350 bp in the region between the pol and env genes. The SIVAGM was apparently derived from cell cultures infected with a macaque isolate, SIVMAC-251. The contamination provides an opportunity to measure the maximum rate of evolution in the SIVAGM by comparing its DNA sequence to those of SIVMAC-251 and SIVMAC-142. The analysis shows that the rates are given approximately by (1.95 +/- 1.37) x 10(-3)/site/year for one SIVAGM sequence and (5.18 +/- 2.25) x 10(-3)/site/year for another.
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PMID:Molecular evolution of the human and simian immunodeficiency viruses. 246 34

The lily retrotransposon del 1-46 is 9345 base pairs (bp) long. It has long terminal repeats (LTRs) of 2406 bp (left) and 2415 bp (right), which differ in sequence by 1.4%. Sequences similar to those involved in priming DNA synthesis in retroviruses occur in the internal region. Near the left LTR is a sequence complementary to 18 residues at the 3' end of methionine initiator tRNA of three plant species, and a run of 12 purines occurs close to the right LTR. One internal reading frame of del 1-46 has relatively few stop codons. The 1462-codon product from this frame has motifs, in N to C terminus order, corresponding to those identified with RNA binding, protease, reverse transcriptase, RNase H, and integrase functions in retroviruses and certain other retrotransposons. Amino acid sequence comparisons of three conserved pol regions show del to be closely related to the Ty3 retrotransposon of yeast (37-40% identity). del is also related to the gypsy group of Drosophila (17.6, 297, gypsy/mdg4, and 412), showing closer identity with their reverse transcriptase (32-38%) and RNase H (36-45%) domains than with their integrase domain (21-26%). It is proposed that a gypsy group ancestor exchanged the integrase region with a more distantly related element since its divergence from a del/Ty3 common ancestor. The occurrence of related retrotransposons in three different kingdoms (plants, animals, and fungi) strongly implies their horizontal transmission in recent evolutionary time.
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PMID:Plant retrotransposon from Lilium henryi is related to Ty3 of yeast and the gypsy group of Drosophila. 254 87


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