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 effects of AZTMP and other nucleoside 5'-monophosphates on the RNA-dependent DNA polymerase and RNase H activities of a recombinant HIV reverse transcriptase have been investigated. Both activities are sensitive to inhibition by millimolar concentrations of AZTMP with MgCl2 as divalent cation activator. Substitution of Mn2+ for Mg2+ markedly potentiates the inhibition of RNase H activity by AZTMP, reducing the IC50 from 5 to 0.05 mM. In contrast, Mn2+ does not alter the sensitivity of the RNA-dependent DNA polymerase activity to inhibition by AZTMP. The inhibition of RNase H activity by AZTMP can be reversed by increasing concentrations of the substrate poly(A)/poly(dT), suggesting that AZTMP may compete with the substrate for binding at the active site of RNase H. Other nucleoside 5'-monophosphates do not inhibit RNase H in the presence of Mg2+. However, in the presence of Mn2+, deoxy- and dideoxynucleoside 5'-monophosphates that are complementary to the DNA strand of the heteroduplex substrate are somewhat inhibitory. The RNA-dependent DNA polymerase activity is a slightly inhibited by AZTMP and ddTMP in either Mg2+ or Mn2+, and substitution of Mn2+ for Mg2+ results in inhibition by ddAMP as well. Naturally occurring ribo- or deoxyribonucleoside 5'-monophosphates are not inhibitory at concentrations up to 5 mM. Since AZTTP inhibits the RNA-dependent DNA polymerase activity of HIV reverse transcriptase at nanomolar concentrations, it is unlikely that the inhibition of this activity by AZTMP plays a significant role in the antiviral effect of AZT. However, the inhibition of the RNase H activity by AZTMP, which can reach millimolar concentrations in vivo, may account for part of the sensitivity of the virus to AZT.
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PMID:Inhibition of the RNase H activity of HIV reverse transcriptase by azidothymidylate. 170 9

Five cassettes of the pol gene of human immunodeficiency virus 1 were constructed and inserted under the control of the polyhedrin gene promoter of Autographa californica nuclear polyhedrosis virus by homologous recombination. The first cassette polF contains the full-length pol open reading frame; the second cassette pol100 starts with the first AUG codon of the pol gene and deletes 103 amino acids from the amino terminus of the pol gene product; the third cassette pol97 deletes the entire protease coding sequence; the fourth cassette pol66 deletes both the protease and endonuclease/integrase coding sequences; and the fifth cassette pol51 contains the reverse transcriptase coding sequences plus 39 3'-terminal nucleotides of the RNase H coding sequences. We have expressed these five forms of the pol gene in Spodoptera frugiperda SF9 cells and have analyzed for both reverse transcriptase and RNase H activities. The polF construct expressed several processed forms, 66 kDa, 51 kDa, and 34 kDa proteins, that were detected only by Western blot. In contrast, pol100, pol97, pol66, and pol51 products were expressed at high levels and were readily detectable in gels by staining. The levels of expression of these four products were estimated to be greater than 150 mg/liter of culture (5 x 10(8) cells). Activity gel analyses showed that the pol100, pol97, pol66, and pol51 products possess reverse transcriptase activity; however, only pol97 and pol66 have RNase H activity. Our results demonstrate that many forms, including partially cleaved forms of human immunodeficiency virus 1 pol gene products, possess reverse transcriptase activity but only certain forms have RNase H activity.
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PMID:Enzyme activities in four different forms of human immunodeficiency virus 1 pol gene products. 171 Dec 3

The reverse transcriptase of human immunodeficiency virus type 1 is a heterodimeric protein consisting of two polypeptides with masses of 66 and 51 kDa and has, as a second enzymatic activity, RNase H activity. The 66-kDa polypeptide can be cleaved by the virus-encoded protease to yield polypeptides of 51 and 15 kDa. The latter has been characterized as possessing RNase H activity [Hansen, J., Schultze, T., Mellert, W. & Moelling, K. (1988) EMBO J. 7, 239-243]. We have purified simultaneously the heterodimeric reverse transcriptase/RNase H containing the 66/51-kDa polypeptides and the 15-kDa RNase H from Escherichia coli containing the expression vector pJS 3.7 by a procedure including chromatography on DEAE-cellulose, phosphocellulose, and heparin-Sepharose. Two RNase H and reverse transcriptase peaks were separated on phosphocellulose, one coinciding with the heterodimeric protein and the other with the 15-kDa protein. On the basis of the following findings it appears that the 15-kDa polypeptide has both RNase H and reverse transcriptase activities: (i) it copurified with both activities; (ii) it functioned as a reverse transcriptase in an in situ assay after SDS/polyacrylamide gel electrophoresis; (iii) polyclonal antibodies raised against the 66-kDa polypeptide reacted in immunoblots exclusively with a 15-kDa polypeptide, reacted in immunoblots exclusively with a 15-kDa polypeptide, while no immunoreactive bands in the range of 51-66 kDa were seen in the 15-kDa polypeptide preparation; (iv) the p15 and the p66/51 reverse transcriptase could be quantitatively pelleted in an enzymatically active form only when antibodies specific for the p66 carboxyl terminus were used; and (v) the p15 protein had bona fide properties of a reverse transcriptase and could enzymatically synthesize a high molecular weight, alkali-resistant product. The two reverse transcriptases appear to have different behaviors on various template/primer systems tested. Conceivably different forms of human immunodeficiency virus type 1 reverse transcriptases might be used in individual steps of (+)- and (-)-strand replication.
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PMID:The p15 carboxyl-terminal proteolysis product of the human immunodeficiency virus type 1 reverse transcriptase p66 has DNA polymerase activity. 171 Dec 22

HIV reverse transcriptase (RT) is the target of the most widely used treatments for AIDS. Biochemical and mutagenesis studies performed on HIV-1 RT are reviewed in light of the enzyme's structure and functions. Features described include domain arrangement, dimerization, proteolytic processing, and specific recognition of the priming tRNA. Possible regions of functional importance as determined by comparative amino acid sequence analysis and by site-directed mutagenesis are identified. Among the conclusions of the analysis is the unexpected realization that the substrate for proteolytic maturation of the HIV-1 RT p66/p66 homodimer to the p66/p51 heterodimer is most likely an unfolded RNase H domain. In addition, the current progress in crystallization and structure determination of HIV-1 RT is described. Finally, a functional-model of the active reverse transcription complex is presented.
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PMID:HIV reverse transcriptase structure-function relationships. 171 68

We have labeled the primer binding domain of murine leukemia virus reverse transcriptase (MuLV RT) by covalently cross-linking 5' end labeled d(T)8 to MuLV RT, using ultraviolet light energy. The specificity and the functional significance of the primer cross-linking reaction were demonstrated by the fact that (i) other oligomeric primers, tRNAs, and also template-primers readily compete with radiolabeled d(T)8 for the cross-linking reaction, (ii) under similar conditions, the competing primers and template-primer also inhibit the DNA polymerase activity of MuLV RT to a similar extent, (iii) substrate deoxynucleotides have no effect, and (iv) the reaction is sensitive to high ionic strength. In order to identify the primer binding domains/sites in MuLV RT; tryptic digests prepared from the covalently cross-linked MuLV RT and [32P]d(T)8 complexes were resolved on C-18 columns by reverse-phase HPLC. Three distinct radiolabeled peptides were found to contain the majority of the bound primer. Of these, peptide I contained approximately 65% radioactivity, while the remainder was associated with peptides II and III. Amino acid composition and sequence analyses of the individual peptides revealed that peptide I spans amino acid residues 72-80 in the primary amino acid sequence of MuLV RT and is located in the polymerase domain. The primer cross-linking site appears to be at or near Pro-76. Peptides II and III span amino acid residues 602-609 and 615-622, respectively, and are located in the RNase H domain. The probable cross-linking sites in peptides II and III are suggested to be at or near Leu-604 and Leu-618, respectively.
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PMID:Photoaffinity labeling of the primer binding domain in murine leukemia virus reverse transcriptase. 171 70

The template mRNA was extracted from Schistosoma japonicum. The first strand of cDNA was synthesized by AMV-reverse transcriptase. The second strand cDNA was first digested by RNase H to remove mRNA and was then synthesized by AMV-reverse transcriptase, T4-DNA polymerase. Sizing of cDNA was applied on a NACS column to remove small fragments of less than 1 kb. Homopolymeric tailing of vector (pUC18) was done with dGTP and DNA terminal transferase and tailing of the cDNA with dCTP was carried out under the same conditions. After annealing, the plasmids with cDNA were transformed into E. coli MC1061. The efficiency of cloning was about 10(4)/micrograms mRNA with 30% of the transformants having the inserts of cDNA (Figs. 1-2).
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PMID:[Construction of a cDNA library of Schistosoma japonicum]. 171 36

Purified recombinant reverse transcriptase (RT) from human immunodeficiency virus type 1 (HIV-1) was used to raise 21 monoclonal antibodies with anti-RT specificities. The antibodies were characterized using Western blotting against native virus and recognized either the p66 or p66, p51 components of RT. Further immunoblotting using either cyanogen bromide fragmented RT or truncated mutants of RT along with cross-competition studies enabled the location of various immunogenic regions of RT to be identified. Three antibodies recognized a linear epitope in the N-terminal region (amino acids 128-176). Also, a neutralizing RT antibody recognized a conformational epitope in this region. Three monoclonals had epitopes mapped to linear sequences in the RNase H region at the C-terminus of the RT. Another neutralizing antibody, also requiring folding of the RT protein had its epitope more centrally located (231-353). Of the remaining 13 monoclonals, 7 were roughly located in the C-terminal region and required folding of the protein for epitope recognition and only three of the remaining six could be mapped to conformational epitopes in N-terminal and central regions of the RT. None of the antibodies tested recognized HIV-2 RT products p68 and p55 in Western blot.
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PMID:Monoclonal antibodies define linear and conformational epitopes of HIV-1 pol gene products. 171 17

The reverse transcriptase/RNase H of HIV-1 is composed of a p66/p51 heterodimer when analyzed from virus particles. A recombinant reverse transcriptase (RT)/RNase H which after purification consisted mainly of p66 was analyzed as substrate of the purified recombinant HIV-1 protease p9 in vitro. The p66 protein if treated with the protease is processed to a stable p66/p51 heterodimer. A p15 protein is a prominent cleavage product which was identified as the carboxyterminal portion of p66 by means of a monoclonal antibody. It exhibits RNase H activity when tested by activated gel analysis. Presence of SDS during the incubation allowed complete degradation of p66 depending on the conditions, which indicates that conformation of a substrate is relevant for cleavage by the HIV-1 protease. A synthetic heptapeptide AET-FYVD derived from the region between RT and RNase H is cleaved efficiently in vitro by the HIV-1 protease at the F'Y junction, and may mimick a natural cleavage site. P66/p51 heterodimers exhibit higher RT and RNase H activities than p66 when renatured from polyacrylamide gels.
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PMID:Cleavage of the HIV-1 p66 reverse transcriptase/RNase H by the p9 protease in vitro generates active p15 RNase H. 171 81

The reverse transcriptase enzymes of retroviruses are multifunctional proteins containing both DNA polymerase activity and a nuclease activity, termed RNase H, specific for RNA in RNA-DNA hybrid form. To determine the role of RNase H activity in retroviral replication, we constructed a series of mutant genomes of Moloney murine leukemia virus that encoded reverse transcriptase enzymes that were specifically altered to retain polymerase function but lack RNase H activity. The mutant genomes were all replication defective. Analysis of in vitro reverse transcription reactions carried out by mutant virions showed that minus-strand strong-stop DNA was formed but did not efficiently translocate to the 3' end of the genome; rather, the DNA was stably retained in RNA-DNA hybrid form. Plus-strand strong-stop DNA was not detected. These results suggest that RNase H normally promotes strong-stop translocation, perhaps by exposing single-stranded DNA sequences for base pairing. Four new DNA species were also detected among the reaction products. Analysis of these DNAs suggested that they were minus-strand DNAs formed from VL30 RNAs encoded by the mouse genome. We suggest that reverse transcriptase can initiate DNA synthesis at any one of four alternate tRNA primer-binding sites near the 5' ends of VL30 RNAs.
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PMID:Abortive reverse transcription by mutants of Moloney murine leukemia virus deficient in the reverse transcriptase-associated RNase H function. 171 62

Two model substrates were prepared to examine the mechanism of tRNA-primer excision catalyzed by reverse transcriptase associated ribonuclease H (RT-RNase H). The first model substrate contained sequences from the HIV genome and was designed to be structurally similar to the DNA-extended tRNA created by initiation of minus-strand DNA synthesis during retroviral replication. The DNA-extended RNA was a template and was annealed to a DNA oligonucleotide that primed reverse transcription of the RNA in the template. The second model substrate was structurally similar the first substrate but contained sequences unrelated to the HIV viral genome. The RT-RNase H catalyzed excision of the RNA from the template of the two model substrates was examined. Human immunodeficiency virus (HIV) and Moloney murine leukemia virus RT-RNase H hydrolyzed the substrates to leave a single ribonucleotide 5'-phosphate at the 5'-terminus of the model DNA genome. In contrast, avian myeloblastosis virus RT-RNase H hydrolyzed the phosphodiester bond at the DNA-RNA junction. These hydrolytic specificities were not highly dependent on substrate sequence. The importance of these specificities to retroviral integration is discussed. Additional data indicated that the HIV polymerase and RNase H active sites are separated by a distance equivalent to the length of a 15-nucleotide RNA-DNA heteroduplex.
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PMID:Human immunodeficiency virus reverse transcriptase ribonuclease H: specificity of tRNA(Lys3)-primer excision. 171 59


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