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)

Functional analysis of naturally occurring hepatitis B virus (HBV) mutations is crucial in understanding their impact on disease. We have recently identified two mutations in the HBV core promoter of an HBV strain associated with fulminant hepatitis leading to highly (15-fold) enhanced replication as a result of increased viral encapsidation of pregenomic RNA into the core particles (T. F. Baumert et al., J. Clin. Invest. 98:2268-2276, 1996). Functional studies in an encapsidation assay had demonstrated that the increase in encapsidation was largely independent of pregenomic RNA transcription. In this study, we define the molecular mechanism whereby the two core promoter mutations (C to T at nucleotide [nt] 1768 and T to A at nt 1770) result in enhanced viral encapsidation and replication. The effect of these mutations leading to increased encapsidation is mediated through enhanced core protein synthesis (15-fold) by the mutant virus. The marked increase in core protein synthesis is largely a result of posttranscriptional or translational effect of the mutations because the mutations resulted in only a twofold increase in pregenomic RNA transcription. In addition, this effect appears to be selective for core expression since reverse transcriptase-polymerase expression was increased only twofold. trans-complementation analyses of HBV replication demonstrated that enhanced replication occurred only when the mutations were provided together with the core protein in trans, confirming the functional association of the core promoter mutations and core protein expression. In addition, the effect of the mutations appears to be quantitatively dependent on the strain background to which the mutations were introduced. Our study suggests that the HBV core promoter regulates core protein expression at both transcriptional and posttranscriptional levels.
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PMID:Naturally occurring mutations define a novel function of the hepatitis B virus core promoter in core protein expression. 965 27

The hepatitis B virus (HBV) and other members of the hepadnaviridae replicate by reverse transcription of an RNA intermediate, pregenomic RNA (pgRNA). pgRNA is also translated into core protein and polymerase (reverse transcriptase) protein. Before being reverse transcribed, pgRNA is sequestrated from the cytoplasm by being packaged, together with polymerase, into subviral particles composed of core protein. For pgRNA to be encapsidated, its 5' end is folded into a stem-loop structure, known as the encapsidation signal or epsilon (epsilon). This stable bipartite stem-loop structure contains a bulge and an apical loop. Besides encapsidation, epsilon is involved in the activation of polymerase, in template restriction and in the initiation of DNA synthesis by reverse transcription. HBV DNA encoding epsilon forms part of the template that is translated into the precore/core fusion protein that is in turn post-translationally modified to produce hepatitis B e antigen (HBeAg). The DNA encoding epsilon may be recombinogenic. Mutations within epsilon can affect its function and sequence conservation within epsilon in natural isolates is therefore high. epsilon could provide a practical target for antiviral therapy.
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PMID:Structure and function of the encapsidation signal of hepadnaviridae. 985 45

Evidence is presented that the previously cloned type I duck interferon (DuIFN) cDNA encodes a homologue of mammalian interferon-alpha (IFN-alpha). Recombinant DuIFN-alpha was used to study the inhibition of duck hepatitis B virus (DHBV) replication in primary hepatocytes in order to determine the IFN-sensitive steps of the virus replication cycle. IFN-treated cells accumulated two- to threefold-lower amounts of viral RNA transcripts early during infection, when IFN was added before virus. This reduction was not due to inhibition of virus entry since initial covalently closed circular DNA levels were not decreased in IFN-treated cells. Interestingly, the inhibitory effect of IFN on viral RNA levels was not observed in cells infected with a mutant DHBV that fails to synthesize core protein, suggesting that an uncharacterized core protein-mediated enhancing effect is blocked by IFN. When IFN was added at 4 days postinfection, encapsidated viral RNA pregenomes disappeared from infected cells within 3 days. This depletion was not simply due to conversion of pregenomes to DNA since depletion was not blocked by phosphonoformic acid, an inhibitor of the viral reverse transcriptase. The intracellular concentration of intact nucleocapsids was reduced, suggesting that in the presence of IFN pregenome-containing capsids were selectively depleted in hepatocytes. Thus, two steps in DHBV replication that involve the viral core protein were inhibited by DuIFN-alpha.
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PMID:Elimination of duck hepatitis B virus RNA-containing capsids in duck interferon-alpha-treated hepatocytes. 1036 93

The role of avian eggshell matrix proteins in shell formation is poorly understood. This calcitic biomaterial forms in a uterine fluid where the protein composition varies during the initial, calcification, and terminal phases of eggshell deposition. A specific antibody was raised to a 116-kDa protein, which is most abundant in uterine fluid during active eggshell calcification. This antiserum was used to expression screen a bacteriophage cDNA library prepared using mRNA extracted from pooled uterine tissue harvested at the midpoint of eggshell calcification. Plasmids containing inserts of differing 5'-lengths were isolated with a maximum cDNA sequence of 2.4 kilobases. Northern blotting and reverse transcriptase-polymerase chain reaction demonstrated that the 2. 35-kilobase message was expressed in a uterine-specific manner. The hypothetical translational product from the open reading frame corresponded to a novel 80-kDa protein, which we have named ovocleidin-116. After removal of the predicted signal peptide, its N-terminal sequence corresponded almost exactly with that determined from direct microsequencing of the 116-kDa uterine protein (this work) and with that previously determined for the core protein of a 120-kDa eggshell dermatan sulfate proteoglycan (Corrino, D. A., Rodriguez, J. P., and Caplan, A. I. (1997) Connect. Tissue Res. 36, 175-193). Ultrastructural colloidal gold immunocytochemistry of ovocleidin-116 demonstrated its presence in the organic matrix, in small vesicles found throughout the mineralized palisade layer, and the calcium reserve assembly of the mammillary layer. Ovocleidin-116 thus is a candidate molecule for the regulation of calcite growth during eggshell calcification.
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PMID:Molecular cloning and ultrastructural localization of the core protein of an eggshell matrix proteoglycan, ovocleidin-116. 1055 57

It has been reported that MUC2 mucin is expressed in goblet cells of gastric intestinal metaplasia, but not in its normal epithelium. To confirm this finding, we have examined the expression of the MUC2 gene by reverse transcriptase-polymerase chain reaction and immunohistochemical methods in gastric tissues obtained by routine upper gastrointestinal tract endoscopy and compared the results with pathological findings based on hematoxylin and eosin (H&E) staining. In 16.7% of the tissue specimens tested, MUC2 mRNA was detected in spite of the absence of intestinal metaplasia in HE specimens. A possible explanation for this was the identification by immunohistochemistry of MUC2 protein in regenerative gastric mucosal cells in biopsies that did not contain intestinal metaplasia. Sialyl-Le(x) epitope, which is suggested to be located on MUC2 mucin core protein (MUC2 protein), was also immunohistochemically detected in both goblet cells of intestinal metaplasia and regenerative epithelium. With regard to carcinoma, MUC2 protein was predominantly expressed in intestinal-type adenocarcinoma. These data indicate that MUC2 mucin is expressed in gastric regenerative epithelium in addition to intestinal metaplasia and intestinal type adenocarcinoma.
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PMID:Expression of MUC2 gene in gastric regenerative, metaplastic, and neoplastic epithelia. 1063 92

The hepadnavirus reverse transcriptase binds cotranslationally to the viral pregenomic RNA. This ribonucleoprotein complex is then encapsidated into nascent viral core particles, where the reverse transcriptase copies the viral RNA into DNA. Here we report that 75% of the duck hepatitis B virus reverse transcriptase present in transfected LMH cells does not follow this well-known pathway but rather exists in the cell separate from the core protein or nucleocapsids. The nonencapsidated reverse transcriptase is also abundant in infected duck liver. The nonencapsidated reverse transcriptase exists as a complex set of isoforms that are most likely produced by posttranslational modification. Interestingly, only the smallest of these isoforms is encapsidated into viral core particles. The nonencapsidated reverse transcriptase is bound to a large cellular cytoplasmic structure(s) in a detergent-sensitive complex. The cellular distribution of the reverse transcriptase only partially overlaps that of the core protein, and this distribution is unaffected by blocking encapsidation. These observations raise the possibilities that the metabolic fate of the reverse transcriptase may be posttranscriptionally regulated and that the reverse transcriptase may have roles in the viral replication cycle beyond its well-known function in copying the viral genome.
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PMID:The majority of duck hepatitis B virus reverse transcriptase in cells is nonencapsidated and is bound to a cytoplasmic structure. 1095 66

Human UDP-d-xylose:proteoglycan core protein beta-d-xylosyltransferase (EC 2.4.2.26, XT-I) initiates the biosynthesis of glycosaminoglycan chains in proteoglycans by transferring xylose from UDP-xylose to specific serine residues of the core protein. Based on the partial amino acid sequence of the purified enzyme from human JAR choriocarcinoma cell culture supernatant we isolated a cDNA encoding XT-I using the degenerate reverse transcriptase-polymerase chain reaction method. This enzyme, which is involved in chondroitin sulfate, heparan sulfate, heparin and dermatan sulfate biosynthesis, belongs to a novel family of glycosyltransferases with no homology to proteins known so far. 5' and 3'-RACE were performed to isolate a novel cDNA fragment of 3726 bp with a single open reading frame encoding at least 827 amino acid residues with a molecular mass of 91 kDa. The human XT-I gene was located on chromosome 16p13.1 using radiation hybrid mapping, and extracts from CHO-K1 cells transfected with the XT-I cDNA in an expression vector exhibited marked XT activity. A new 3608 bp cDNA fragment encoding a protein of 865 amino acid residues was also isolated by PCR using degenerate primers based on the amino acid sequence of human XT-I. The amino acid sequence of this XT-II isoform displayed 55% identity to the human XT-I. The XT-II gene was located on chromosome 17q21.3-17q22, and the exon/intron structure of the 15 kb gene was determined. RT-PCR analyses of XT-I and XT-II mRNA from various tissues confirmed that both XT-I and XT-II transcripts are ubiquitously expressed in the human tissues, although with different levels of transcription. Furthermore, the cDNAs encoding XT-I and XT-II from rat were cloned. The deduced amino acid sequences of rat xylosyltransferases displayed 94% identity to the corresponding human enzyme.
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PMID:Molecular cloning and expression of human UDP-d-Xylose:proteoglycan core protein beta-d-xylosyltransferase and its first isoform XT-II. 1109 77

Jule is the second complete long-terminal-repeat (LTR) Ty3/Gypsy retrotransposon identified to date in vertebrates. Jule, first isolated from the poeciliid fish Xiphophorus maculatus, is 4.8 kb in length, is flanked by two 202-bp LTRs, and encodes Gag (structural core protein) and Pol (protease, reverse transcriptase, RNase H, and integrase, in that order) but no envelope. There are three to four copies of Jule per haploid genome in X. maculatus. Two of them are located in a subtelomeric region of the sex chromosomes, where they are associated with the Xmrk receptor tyrosine kinase genes, of which oncogenic versions are responsible for the formation of hereditary melanoma in Xiphophorus. One almost intact copy of Jule was found in the first intron of the X-chromosomal allele of the Xmrk proto-oncogene, and a second, more corrupted copy is present only 56 nt downstream of the polyadenylation signal of the Xmrk oncogene. Jule-related elements were detected by Southern blot hybridization with less than 10 copies per haploid genome in numerous other poeciliids, as well as in more divergent fishes, including the medakafish Oryzias latipes and the tilapia Oreochromis niloticus. Database searches also identified Jule-related sequences in the zebrafish Danio rerio and in both genome project pufferfishes, Fugu rubripes and Tetraodon nigroviridis. Phylogenetic analysis revealed that Jule is the first member of the Mag family of Ty3/Gypsy retrotransposons described to date in vertebrates. This family includes the silkworm Mag and sea urchin SURL retrotransposons, as well as sequences from the nematode Caenorhabditis elegans. Additional related elements were identified in the genomes of the malaria mosquito Anopheles gambiae and the nematode Ascaris lumbricoides. Phylogeny of Mag-related elements suggested that the Mag family of retrotransposons is polyphyletic and is constituted of several ancient lineages that diverged before their host genomes more than 600 MYA.
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PMID:Jule from the fish Xiphophorus is the first complete vertebrate Ty3/Gypsy retrotransposon from the Mag family. 1115 69

Thai bitter gourd protein (MRK29) was isolated from Momordica charantia ripe fruit and seed. The purification was performed by ammonium sulfate fractionation and gel filtration chromatography. MRK29 possessed one isoelectric point of (pI) > or = 9, and the time of flight mass spectrum (TOFMS) indicated its molecular weight at 28.6 kD. The twenty amino acid sequence from the N-terminus was in the following order: 1Asp Val Asn Phe Arg Leu Ser Gly Ala 10Asp Pro Arg X Tyr Gly Met Phe Ile Glu 20Asp. MRK29 inhibited the HIV-1 reverse transcriptase with 50% IR at the concentration of 18 micrograms/ml. MRK29 was concentrated in the 30-60% salt precipitated fraction, at which the concentration of 0.175 microgram/ml exerted 82% reduction of viral core protein p24 expression in HIV-infected cells. MRK29 might have modulatory role on immune cells, because it increased 3-fold TNF activity.
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PMID:HIV inhibitor from Thai bitter gourd. 1145 53

Dentin sialoprotein (DSP) is a major glycoprotein present in the mineralized dentin matrix that is expressed mainly by young and mature odontoblasts. Mutations in the DSP coding regions are linked to Dentinogenesis imperfecta I and II. indicating the importance of DSP in tooth formation. Previous studies have identified multiple mRNA transcripts in dentin that code for both DSP and phosphophoryns (PPs). Using reverse transcriptase-polymerase chain reaction (RT-PCR) to characterize these mRNA transcripts, we have identified a cDNA that codes for DSP, but not PP. This cDNA codes for a protein with 324 amino acids, 303 amino acids being identical to the published rat DSP sequence. However, the subsequent 21 amino acids are unique to this cDNA. Based on the coding sequence, the core protein is predicted to have a pI=4.24, a net charge of -34, and to contain four potential N-glycosylation sites and six potential sites for phosphorylation by casein kinase. That the corresponding mRNA was present in day 5 molar tooth germs was confirmed using RNA protection assays. These data, therefore, identify a novel transcript in rat tooth germs that codes only for DSP (designated as DSPII).
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PMID:A novel rat dentin mRNA coding only for dentin sialoprotein. 1169 56


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