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)

The Mauriceville and Varkud mitochondrial plasmids of Neurospora are closely related DNA elements whose nucleotide sequences and genetic organization suggest relationships to retrotransposons and mitochondrial introns. Both plasmids potentially encode a reverse transcriptase-like protein of 710 amino acids. We show that mitochondria from the Mauriceville and Varkud strains contain a reverse transcriptase activity highly specific for endogeneous plasmid RNA in RNP preparations. The reverse transcriptase synthesizes full-length minus-strand DNA beginning at the 3' end of the plasmid transcript, which has tRNA-like characteristics similar to the 3' ends of plant viral RNAs. Our results suggest that the plasmids use a novel mechanism of reverse transcription, which may have evolved to utilize tRNA-like structures at the 3' ends of self-replicating RNAs. This mechanism may be ancestral to the standard retroviral mechanism.
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PMID:A novel reverse transcriptase activity associated with mitochondrial plasmids of Neurospora. 246 Feb 46

Pseudouridine (psi), the most common single modified nucleoside in ribosomal RNA, has been positioned in the small subunit (SSU) and large subunit (LSU) RNAs of a number of representative species. Most of the information has been obtained by application of a rapid primed reverse transcriptase sequencing technique. The locations of these psi residues have been compared. Many sites for psi are the same among species, but others are distinct. In general, the percentage psi in multicellular eukaryotes is greater than in prokaryotes. In LSU RNA, the psi residues are strongly clustered in three domains, all of which are near or connected to the peptidyl transferase center. There is no apparent clustering of psi in SSU RNA. The psi sites in LSU RNA overlap those for the methylated nucleosides, but this is not the case in SSU RNA. There are 265 psi sites known to nucleotide resolution, of which 246 are in defined secondary structures, and 112 of these are in nonidentical structural contexts. All 246 psi sites can be classified into five structural types. Two Escherichia coli psi synthases have been cloned and characterized, one for psi 516 in SSU RNA and one for psi 746 in LSU RNA. The psi 746 synthase recognizes free RNA, but the psi 516 enzyme requires an intermediate RNP particle. Possible functional roles for psi in the ribosome are discussed.
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PMID:The pseudouridine residues of ribosomal RNA. 872 7

We examined the genomic structure of the reeler gene in Orleans reeler mouse mutant. Exon skipping of the reeler gene caused a 220 bp deletion in the transcript, resulting in a frame shift of the reeler gene which disrupts the 8th EGF-like motif of the reeler product. Surprisingly, the skipped exon was inserted by the 7104 bp L1 element which carried the full-length stretch of the mouse L1 sequence, consisting of a 212 bp F-type tandem repeat, open reading frame 1 (ORF1), ORF2, the polyadenylation signal and a poly A stretch. The transposed L1 sequence was flanked by 13 bp of the target sequence at both ends. ORF1 and ORF2 of this L1 repeat element are thought to encode a component of the RNP particle and the reverse transcriptase, respectively. Orleans reeler was originally established by spontaneous mutation caused by L1 insertion, and this L1 sequence is considered to be potentially active for transposition in mouse genome.
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PMID:Dysfunction of the Orleans reeler gene arising from exon skipping due to transposition of a full-length copy of an active L1 sequence into the skipped exon. 881 36

The Lactococcus lactis group II intron Ll.ltrB is similar to mobile yeast mtDNA group II introns, which encode reverse transcriptase, RNA maturase, and DNA endonuclease activities for site-specific DNA insertion. Here, we show that the Lactococcal intron can be expressed and spliced efficiently in Escherichia coli. The intron-encoded protein LtrA has reverse transcriptase and RNA maturase activities, with the latter activity shown both in vivo and in vitro, a first for any group II intron-encoded protein. As for the yeast mtDNA introns, the DNA endonuclease activity of the Lactococcal intron is associated with RNP particles containing both the intron-encoded protein and the excised intron RNA. Also, the intron RNA cleaves the sense-strand of the recipient DNA by a reverse splicing reaction, whereas the intron-encoded protein cleaves the antisense strand. The Lactococcal intron endonuclease can be obtained in large quantities by coexpression of the LtrA protein with the intron RNA in E. coli or reconstituted in vitro by incubating the expressed LtrA protein with in vitro-synthesized intron RNA. Furthermore, the specificity of the endonuclease and reverse splicing reactions can be changed predictably by modifying the RNA component. Expression in E. coli facilitates the use of group II introns for the targeting of specific foreign sequences to a desired site in DNA.
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PMID:A bacterial group II intron encoding reverse transcriptase, maturase, and DNA endonuclease activities: biochemical demonstration of maturase activity and insertion of new genetic information within the intron. 935 59

The reverse transcriptase telomerase is a ribonucleoprotein complex that adds telomeric repeats to chromosome ends, using a sequence within its endogenous RNA component as a template. Although templating domains of telomerase RNA have been studied in detail, little is known about the roles of the remaining residues, particularly in yeast. We examined the functions of nontemplate telomerase residues in the telomerase RNA of budding yeast Kluyveromyces lactis. Although approximately half of the RNA residues were dispensable for function, four specific regions were essential for telomerase action in vivo. We analyzed the effects of mutating these regions on in vivo function, in vitro telomerase activity, and telomerase RNP assembly. Deletion of two regions resulted in synthesis of stable RNAs that appeared unable to assemble into a stable RNP. Mutating a region near the 5' end of the RNA allowed RNP assembly but abolished enzymatic activity. Mutations in another specific small region of the RNA led to an inactive telomerase RNP with an altered RNA conformation.
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PMID:Specific telomerase RNA residues distant from the template are essential for telomerase function. 978 2

Group II introns encode proteins with reverse transcriptase activity. These proteins also promote RNA splicing (maturase activity) and then, with the excised intron, form a site-specific DNA endonuclease that promotes intron mobility by reverse splicing into DNA followed by target DNA-primed reverse transcription. Here, we used an Escherichia coli expression system for the Lactococcus lactis group II intron Ll.LtrB to show that the intron-encoded protein (LtrA) alone is sufficient for maturase activity, and that RNP particles containing only the LtrA protein and excised intron RNA have site-specific DNA endonuclease and target DNA-primed reverse transcriptase activity. Detailed analysis of the splicing reaction indicates that LtrA is an intron-specific splicing factor that binds to unspliced precursor RNA with a K(d) of </=0.12 pM at 30 degrees C. This binding occurs in a rapid bimolecular reaction, which is followed by a slower step, presumably an RNA conformational change, required for splicing to occur. Our results constitute the first biochemical analysis of protein-dependent splicing of a group II intron and demonstrate that a single intron-encoded protein can interact with the intron RNA to carry out a coordinated series of reactions leading to splicing and mobility.
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PMID:RNA and protein catalysis in group II intron splicing and mobility reactions using purified components. 1041 81

The ribonucleoprotein enzyme telomerase extends chromosome ends by copying a specific template sequence within its integral RNA component. An active recombinant telomerase RNP is minimally composed of this RNA and the telomerase reverse transcriptase (TERT) protein, which contains sequence motifs conserved among viral reverse transcriptases (RTs), flanked by N- and C-terminal extensions specific to TERTs. We have used site-directed mutagenesis to explore the roles of Tetrahymena TERT in determining features of telomerase activity in general and in establishing the boundaries and use of an internal RNA template in specific. We identify a new ciliate-specific motif in the TERT N-terminus required for template definition. Moreover, several residues in reverse transcriptase motifs 1, 2, A and D are critical for specific aspects of internal template use. Our results indicate that the unique specificity of telomerase activity is conferred to a reverse transcriptase active site by TERT residues both within and beyond the RT motif region.
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PMID:Template definition by Tetrahymena telomerase reverse transcriptase. 1094 24

Telomeres are stabilized, and telomeric DNA is replenished, by the action of the ribonucleoprotein reverse transcriptase telomerase. Telomere capping functions include the ability of telomeres to protect chromosome ends from cellular DNA-damage responses such as cell cycle arrest or apoptosis. This property of telomeres is especially important for cancer cells, which continue proliferating despite chromosome aberrations. Telomere capping is influenced by multiple, mutually reinforcing factors including telomere length, although telomere length is only one of several determinants of telomere functionality. For example, many cancer cells express high levels of telomerase yet maintain relatively short telomeres. We consider three aspects of telomere capping that have emerged relatively recently: (1) a new role for telomerase in telomere capping independent of its function in telomere elongation. Support for this novel function comes from experiments showing an increase in replicative potential with the reactivation of telomerase, without net telomere lengthening; (2) the role at telomeres of DNA damage proteins. We propose a model in which two factors specifically target telomeres for the action of telomerase, as opposed to recombination or non-homologous end-joining: binding by telomeric proteins that limits DNA damage responses at telomeres, and the affinity of the telomerase RNP for telomeric proteins and DNA; and (3) we discuss a potential protective role of amplified subtelomeric DNAs, which may aid capping of telomeres maintained by non-telomerase based mechanisms through the formation of heterochromatin.
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PMID:New ways not to make ends meet: telomerase, DNA damage proteins and heterochromatin. 1185 Jul 80

Defensins are antimicrobial peptides that play a major role in innate immunity. Using reverse transcriptase-polymerase chain reaction, immunochemistry, or both, we performed a search of all presently known defensins in rat testis, epididymis, and isolated testicular cells; in mouse testis and epididymis; and in human testis and ejaculates. In the rat, all alpha- and beta-defensins except RNP-4 were expressed within the testis, whereas alpha-defensins RNP1-2, RNP-4, and beta-defensins RBD-1 and RBD-2 were present within the epididymis. In the mouse, the cryptdin transcripts CRS1C, mBD-1, and mBD-2 were detected in the testis and epididymis, whereas mBD-3 and mBD-4 were expressed only in the epididymis, and CRS4C was absent in both organs. In the human testis, transcripts for four known defensins were expressed with the consistent exception of HBD-2 and HBD-3. In rat interstitial tissue, resident macrophages expressed most of the defensins studied, whereas Leydig cells produced only RBD-2. In contrast, all studied defensins except RNP-4 were present in the seminiferous tubules. Within these tubules, peritubular and Sertoli cells expressed most of the studied alpha- and beta-defensins, whereas spermatogonia displayed only alpha-defensins, but at relatively high levels. Meiotic pachytene spermatocytes expressed only beta-defensins, whereas postmeiotic spermatids and their cytoplasmic lobes displayed both types. In humans, the HBD-1 peptide was expressed mainly in the germ line from pachytene spermatocytes to late spermatids. The peptide was also present in ejaculated spermatozoa and seminal plasma, where multiple soluble forms were present. Finally, high salt concentration or dithiothreitol-sensitive cationic extracts from human seminal plasma were indeed found to display antimicrobial activity. We conclude that the male reproductive tract produces defensins that most probably assume an important, innate organ defense system against pathogens.
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PMID:Expression of antimicrobial defensins in the male reproductive tract of rats, mice, and humans. 1249

Mobile group II introns encode multidomain proteins with maturase activity involved in splicing and reverse transcriptase (RT) and (often) endonuclease activities involved in intron mobility. These activities are present in a ribonucleoprotein complex that contains the excised intron RNA and the intron-encoded protein. Here, we report biochemical studies of the protein encoded by the group IIA1 intron in the cob gene of fission yeast Schizosaccharomyces pombe mitochondria (cobI1). RNP particle fractions from the wild-type fission yeast strain with cobI1 in its mtDNA have RT activity even without adding an exogenous primer. Characterization of the cDNA products of such reactions showed a strong preference for excised intron RNA as template. Two main regions for initiation of cDNA synthesis were mapped within the intron, one near the DIVa putative high-affinity binding site for the intron-encoded protein and the other near domain VI. Adding exogenous primers complementary to cob exon 2 sequences near the intron/exon boundary stimulated RT activity but mainly for pre-mRNA rather than mRNA templates. Further in vitro experiments demonstrated that cobI1 RNA in RNP particle fractions can reverse splice into double-stranded DNA substrates containing the intron homing site. Target DNA primed reverse transcription was not detected unless a DNA target was used that was already nicked in the antisense strand of exon 2. This study shows that S.pombe cobI1 encodes RNP particles that have most of the biochemical activities needed for it to be a retroelement. Interestingly, it appears to lack an endonuclease activity, suggesting that the active homing exhibited by this intron in crosses may differ somewhat from that of the better-characterized introns.
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PMID:Reverse transcriptase and reverse splicing activities encoded by the mobile group II intron cobI1 of fission yeast mitochondrial DNA. 1275 69


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