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)

delta-Crystallin is the major component of the lenses of most birds and reptiles. In the chicken there are two closely linked, tandemly oriented genes. Almost all of the delta-crystallin of the embryonic chicken lens is produced by the 5' delta 1 gene. This high lens activity has been attributed to an enhancer in intron 3. The 3' delta 2 gene encodes the enzyme argininosuccinate lyase (ASL) which is expressed at a low level in the chicken lens. Both chicken delta-crystallin genes are also expressed slightly in heart and brain, with ASL/delta 2 predominating over delta 1. In the duck (Anas platyrhynchos), ASL/delta 2-crystallin serves as both enzyme and crystallin, resulting in very high levels of ASL activity in the lens. Here we show by genomic cloning that the ASL/delta- crystallin locus is highly conserved between duck and chicken, with the two duck delta-crystallin genes closely linked in tandem. The 4.6 kbp intergenic spacer in the duck locus is 79% identical to the 4 kbp chicken spacer, except for the existence of a 615 bp CR1 element, highly reiterated in the duck genome, 1.8 kbp upstream of the duck ASL/delta 2 gene. The CR1 sequence is a truncated LINE element containing the 3' half of an open reading frame for a retroviral pol-like reverse transcriptase. Sequence analysis revealed (i) that intron 3 of the duck ASL/delta 2 gene is very similar (80%) to intron 3 of the chicken delta 1 and ASL/delta 2 genes, especially in the region of the chicken delta 1 enhancer core (93% identical) and (ii) that the 3' boundary of exon 2 of the duck ASL/delta 2 gene has undergone a recent splice-site slippage event, resulting in a two amino acid insertion in the encoded polypeptide. Finally, reverse transcription/polymerase chain reaction experiments established that both delta-crystallin genes are equally expressed to a high level in the embryonic duck lens; by contrast, both delta-crystallin genes produce a low amount of mRNA in the heart and brain of the embryonic duck, with the enzymatically active ASL/delta 2 being preferentially expressed.
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PMID:Linkage and expression of the argininosuccinate lyase/delta-crystallin genes of the duck: insertion of a CR1 element in the intergenic spacer. 789 58

Short interspersed repetitive elements (SINEs) are a type of retroposon, being members of a class of informational molecules that are amplified via cDNA intermediates and flow back into the host genome. In contrast to retroviruses and retrotransposons, SINEs do not encode the enzymes required for their amplification, such as reverse transcriptases, so they are presumed to borrow these enzymes from other sources. In the present study, we isolated a family of long interspersed repetitive elements (LINEs) from the turtle genome. The sequence of this family was found to be very similar to those of the avian CR1 family. To our surprise, the sequence at the 3' end of the LINE in the turtle genome was nearly identical to that of a family of tortoise SINEs. Since CR1-like LINEs are widespread in birds and in many other reptiles, including the turtle, and since the tortoise SINEs are only found in vertical-necked turtles, it seems possible that the sequence at the 3' end of the tortoise SINEs might have been generated by recombination with the CR1-like LINE in a common ancestor of vertical-necked turtles, after the divergence of side-necked turtles. We extended our observations to show that the 3'-end sequences of families of several tRNA-derived SINEs, such as the salmonid HpaI family, the tobacco TS family, and the salmon SmaI family, might have originated from the respective LINEs. Since it appears reasonable that the recognition sites of LINEs for reverse transcriptase are located within their 3'-end sequences, these results provide the basis for a general scheme for the mechanism by which SINEs might acquire retropositional activity. We propose here that tRNA-derived SINEs might have been generated by a recombination event in which a strong-stop DNA with a primer tRNA, which is an intermediate in the replication of certain retroviruses and long terminal repeat retrotransposons, was directly integrated at the 3' end of a LINE.
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PMID:The 3' ends of tRNA-derived short interspersed repetitive elements are derived from the 3' ends of long interspersed repetitive elements. 866 92

Rat oligodendrocytes spontaneously activate complement (C) and lack the C inhibitor CD59. As a consequence, rat oligodendrocytes are susceptible to lysis by autologous C in vitro. Expression of C inhibitors on human oligodendrocytes in vitro and other human glia has yet to be well characterized. We have previously shown expression at the mRNA level of the membrane inhibitors CD59, decay-accelerating factor (DAF; CD55) and membrane cofactor protein (MCP; CD46) in human astrocytes. We here examine the expression of membrane and secreted C inhibitors by the oligodendrocyte cell line, HOG. HOG cells abundantly expressed CD59, assessed at protein and mRNA level, and expressed DAF and MCP, albeit at a lower level. Expression of all three inhibitors was enhanced by incubation with interferon-gamma or with phorbol ester (PMA). Complement receptor type 1 (CR1; CD35) was neither expressed constitutively nor induced by cytokines. HOG also constitutively secreted C1-inhibitor, S-protein and clusterin. Factor H was secreted only after stimulation with cytokines. C4b binding protein was expressed at a very low level and was detected only at the mRNA level by reverse transcriptase-polymerase chain reaction (RT-PCR). For comparison, astrocyte expression of CD59, DAF, MCP and CR1 was confirmed at the mRNA and protein levels. HOG did not activate C spontaneously, as judged by the lack of deposition of C fragments, and were not lysed by C even after inhibition of CD59 and DAF using specific monoclonal antibodies.
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PMID:Complement regulatory protein expression by a human oligodendrocyte cell line: cytokine regulation and comparison with astrocytes. 895 45

The complement peptide C3a desarg is identical to acylation-stimulating protein (ASP), a human plasma protein that potently stimulates adipocyte triacylglycerol synthesis and glucose transport. Both human and murine adipocytes express mRNA and/or protein for the complement components C3 and factors B and D (adipsin) required to generate ASP. However, the regulatory mechanisms controlling this process are unknown. We have established a semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) technique to demonstrate the presence in mouse 3T3-L1 adipocytes of mRNA for all components of the alternative pathway, including the control proteins factors I and H, CR1 and properdin. On differentiation, mRNA for C3 (fivefold) and factor D (> 50-fold) increased, whereas stimulation with tumour necrosis factor (TNF)-alpha and interleukin (IL) 1 beta led to eightfold increases in factor B mRNA. Metabolic labelling followed by immunoprecipitation showed that factor B protein is normally present in small quantities, and is greatly increased by cytokine stimulation. The larger quantities of C3 and H proteins present were little affected, whereas levels of C3a increased on cytokine stimulation. These results suggest that the rate-limiting step in the cytokine-induced production of ASP in adipocytes is factor B synthesis.
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PMID:Detection and quantification of the control proteins of the alternative pathway of complement in 3T3-L1 adipocytes. 939 88

CR1 elements are a family of retroposons. They are classified as long interspersed elements (LINEs) or non-long-terminal-repeat (non-LTR) retrotransposons, and they have been found in the genomes of many vertebrates. However, they have been only partially characterized, and only a 2-kb region of the 3' end of chicken CR1 has been sequenced. In the present study, we determined the entire consensus sequence of CR1 elements in the turtle genome, designated PsCR1. The first open reading frame (ORF1) of PsCR1 has two unusual arrangements of Cys residues. One of them includes a zinc finger motif, CX2CX14CX2C. The putative zinc finger has cysteine residues with identical spacing and a similar amino acid composition to those found in the species-specific transcription initiation factors SL1 and TIF-IB. The 5' untranslated region (5' UTR) of PsCR1 contains a sequence similar to part of the human L1 promoter, L1 site A, and several cis elements of the type found in eukaryotic genes. Within a region of about 500 bp, there are nine "E boxes," cis elements that are recognized by the basic helix-loop-helix (bHLH) family of proteins. This observation raises the possibility that cellular transcription factors that bind to these sequences might act in concert to regulate the expression of PsCR1. The extent of the sequence divergence of the 3' UTR of CR1 between species was found to be lower than the rate of nonsynonymous substitutions per site in ORF2, suggesting that a strict functional constraint must exist for this region. This result strongly suggests that the conserved 3'-end sequence of CR1 is the recognition site for the reverse transcriptase of CR1. A discussion is presented of a possible mechanism for the integration of CR1 elements and also of the intriguing possible recruitment of the reverse transcriptase for the retroposition of SINEs.
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PMID:Determination of the entire sequence of turtle CR1: the first open reading frame of the turtle CR1 element encodes a protein with a novel zinc finger motif. 940 32

This study describes the consensus sequence of a full-length (4585bp) non-LTR retrotransposon from the fugu fish, Fugu rubripes. The retrotransposon, termed Maui, is represented by a group of very similar LINE elements found as multiple copies within the fish genome. Two long open reading frames (ORFs) are predicted from the sequence. The first ORF has a domain resembling a novel zinc finger motif recently found in both a turtle and a chicken (CR1) non-LTR retrotransposon. The second ORF includes sequences homologous to the endonuclease, reverse transcriptase and carboxy-terminal domains found in other non-LTR retrotransposons. Sequence comparisons of the predicted translation products of the two ORFs indicate that Maui is most closely related to a class of non-LTR retrotransposons represented by the CR1-like elements (chicken repeat 1 elements) that are present in several avian species and have recently been described in the turtle Platemys spixii. The sequence of the 3' untranslated region also supports this relationship since Maui resembles the CR1 like elements in not having a poly-A tail.
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PMID:A LINE element from the pufferfish (fugu) Fugu rubripes which shows similarity to the CR1 family of non-LTR retrotransposons. 1002 50

Rex1, together with the related BABAR: elements, represents a new family of non-long-terminal-repeat (non-LTR) retrotransposons from fish, which might be related to the CR1 clade of LINE elements. Rex1/BABAR: retrotransposons encode a reverse transcriptase and an apurinic/apyrimidinic endonuclease, which is very frequently removed by incomplete reverse transcription. Different Rex1 elements show a conserved terminal 3' untranslated region followed by oligonucleotide tandem repeats of variable size and sequence. Phylogenetic analysis revealed that Rex1 retrotransposons were frequently active during fish evolution. They formed multiple ancient lineages, which underwent several independent and recent bursts of retrotransposition and invaded fish genomes with varying success (from <5 to 500 copies per haploid genome). At least three of these ancient Rex1 lineages were detected within the genome of poeciliids. One lineage is absent from some poeciliids but underwent successive rounds of retrotransposition in others, thereby increasing its copy number from <10 to about 200. At least three ancient Rex1 lineages were also detected in the genome project fish Fugu rubripes. Rex1 distribution within one of its major lineages is discontinuous: Rex1 was found in all Acanthopterygii (common ancestor in the main teleost lineage approximately 90 MYA) and in both European and Japanese eels (divergence from the main teleost lineage about 180 MYA) but not in trout, pike, carp, and zebrafish (divergence 100-120 MYA). This might either result from frequent loss or rapid divergence of Rex1 elements specifically in some fish lineages or represent one of the very rare examples of horizontal transfer of non-LTR retrotransposons. This analysis highlights the dynamics and complexity of retrotransposon evolution and the variability of the impact of retrotransposons on vertebrate genomes.
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PMID:Multiple lineages of the non-LTR retrotransposon Rex1 with varying success in invading fish genomes. 1107 55

The evolution of the novel L2 clade of non-long terminal repeat (LTR) retrotransposons and their evolutionary dynamics in Deuterostomia has been examined. The short-term evolution of long interspersed nuclear element 2s (LINE2s) has been studied in 18 reptilian species by analysis of a PCR amplified 0.7-kb fragment encoding the palm/fingers subdomain of reverse transcriptase (RT). Most of the reptilian LINE2s examined are inactive since they contain multiple stop codons, indels, or frameshift mutations that disrupt the RT. Analysis of reptilian LINE2s has shown a high degree of sequence divergence and an unexpectedly large number of deletions. The evolutionary dynamics of LINE2s in reptiles has been found to be complex. LINE2s are shown to form a novel clade of non-LTR retrotransposons that is well separated from the CR1 clade. This novel L2 clade is more widely distributed than previously thought, and new representatives have been discovered in echinoderms, insects, teleost fishes, Xenopus, Squamata, and marsupials. There is an apparent absence of LINE2s from different vertebrate classes, such as cartilaginous fishes, Archosauria (birds and crocodiles), and turtles. Whereas the LINE2s are present in echinoderms and teleost fishes in a conserved form, in most tetrapods only highly degenerated pseudogenes can be found. The predominance of inactive LINE2s in Tetrapoda indicates that, in the host genomes, only inactive copies are still present. The present data indicate that the vertical inactivation of LINE2s might have begun at the time of Tetrapoda origin, 400 MYA. The evolutionary dynamics of the L2 clade in Deuterostomia can be described as a gradual vertical inactivation in Tetrapoda, stochastic loss in Archosauria and turtles, and strict vertical transmission in echinoderms and teleost fishes.
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PMID:Evolutionary dynamics in a novel L2 clade of non-LTR retrotransposons in Deuterostomia. 1171 71

Perivascular infiltrates composed of macrophages and lymphocytes have been described in lung biopsies of patients displaying pulmonary arterial hypertension (PAH), suggesting that circulating inflammatory cells can be recruited in affected vessels. CX(3)C chemokine fractalkine is produced by endothelial cells and promotes leukocyte recruitment, but unlike other chemokines, it can capture leukocytes rapidly and firmly in an integrin-independent manner under high blood flow. We therefore hypothesized that fractalkine may contribute to pulmonary inflammatory cell recruitment in PAH. Expression and function of the fractalkine receptor (CX(3)CR1) were studied by use of triple-color flow cytometry on circulating T-lymphocyte subpopulations in freshly isolated peripheral blood mononuclear cells from control subjects and patients with PAH. Plasma-soluble fractalkine concentrations were measured by enzyme-linked immunosorbent assay. Finally, fractalkine mRNA and protein expression were analyzed in lung samples by reverse transcriptase-polymerase chain reaction or in situ hybridization and immunohistochemistry, respectively. In patients with PAH, CX(3)CR1 expression and function are upregulated in circulating T-lymphocytes, mostly of the CD4+ subset, and plasma soluble fractalkine concentrations are elevated, as compared with control subjects. Fractalkine mRNA and protein product are expressed in pulmonary artery endothelial cells. We conclude that inflammatory mechanisms involving chemokine fractalkine and its receptor CX(3)CR1 may have a role in the natural history of PAH.
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PMID:CX(3)C chemokine fractalkine in pulmonary arterial hypertension. 1201 93

We have examined complement receptors on human umbilical vein endothelial cells (HUVEC) and found that they express complement receptor 1 (CR1, CD35) and complement receptor 4 (CR4, CD11c/CD18), but not complement receptor 3 (CR3, CD11b/CD18). Binding of monoclonal antibodies against CR1 (CD35) and CR4 (CD11c/CD18) to HUVEC was demonstrated by flow cytometry. The presence of the corresponding mRNAs was confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) and sequencing of the amplified cDNA fragments. When HUVEC were treated with inflammatory mediators, chemotactic agents or the secretagogue phorbol-12-myristate-13-acetate (PMA), no change in reactivity to CR1 (CD35) or CR4 (CD11c/CD18) monoclonal antibodies was detected on the surface of the cells compared with untreated cells. The presence of CR1 (CD35) and CR4 (CD1c/CD18) on HUVEC indicates that endothelial cells (EC) have the potential to bind C3b and iC3b, respectively, which both mediate biological effects in the course of complement activation.
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PMID:Human umbilical vein endothelial cells express complement receptor 1 (CD35) and complement receptor 4 (CD11c/CD18) in vitro. 1208 16


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