Search PubMed⌕ Search

Biomedical subjects

J Hurwitz

Publications and source records attributed to J Hurwitz.

At least 199 records · Page 11Linked to original sources
PubMed1981

Mechanism of mRNA capping by vaccinia virus guanylyltransferase: characterization of an enzyme--guanylate intermediate.

Vaccinia virus RNA guanylyltransferase catalyzes the transfer of GMP from GTP to the 5'-triphosphate or diphosphate terminus of RNA to generate the cap structure G(5')ppp(5')N-. The guanylylation reaction consists of a series of at least two partial reactions: (i) GTP + E in equilibrium E-pG + PPi, (ii) E-pG + (p)ppNpNpN- leads to GpppNpNpN- + E. Inthe first of these, GTP reacts with capping enzyme in the absence of an RNA acceptor to form a covalent enzyme-guanylate intermediate. The GMP is linked to the Mr 95,000 subunit of the capping enzyme via a phosphoamide bond, as judged by the acid-labile, alkali-stable nature of the bond and by the susceptibility of the linkage to cleavage by hydroxylamine at pH 4.75. The isolated enzyme-guanylate complex is able to transfer the guanylate moiety to triphosphate-terminated poly(A) to yield the 5' cap structure GpppA or to pyrophosphate to regenerate GTP. Both partial reactions of transguanylylation require a divalent cation.

Guanosine Monophosphate↗
PubMed1981

Adenovirus DNA replication in vitro: purification of the terminal protein in a functional form.

The 80,000-dalton form of the adenovirus (Ad) terminal protein (pTP) has been purified from Ad-infected HeLa cells. pTP was assayed by its ability to form a covalent complex with dCMP. The protein copurified with an activity that is essential for in vitro Ad DNA replication (Ad protein activity) as well as with a DNA polymerase activity that was distinguished from those of HeLa cell DNA polymerases alpha, beta, and gamma. The Ad protein-associated DNA polymerase activity was detected with activated DNA but not with poly(rA).oligo(dT) as template and was insensitive to aphidicolin and sensitive to N-ethylmaleimide. The Ad protein, DNA polymerase, and pTP-dCMP complex-forming activities sedimented in a glycerol gradient as a single peak with an apparent molecular size of 180,000 daltons. NaDodSO4/polyacrylamide gel analysis of the glycerol gradient fraction showed major bands of 80,000 and 140,000 daltons. The 80,000-dalton band was identified as pTP by comparison of its tryptic peptide map with that of the 55,000-dalton form of the terminal protein, which was purified from Ad virions.

Adenoviruses, Human↗
PubMed1981

Replication of adenovirus DNA-protein complex with purified proteins.

A protein fraction isolated from the cytosol of adenovirus-infected HeLa cells, which contained DNA polymerase alpha, catalyzed adenoviral DNA replication in the presence of adenovirus DNA binding protein, eukaryotic DNA polymerase beta, ATP, all four dNTPs, and MgCl2. DNA replication started at either end of exogenously added adenoviral DNA and was totally dependent on the presence of terminal 55,000-dalton proteins on the DNA template. The replicaton of adenovirus DNA in the system was sensitive to aphidicolin and retained nearly all the properties of DNA replication that occur in vivo or in vitro with crude extracts. The 5'-ends of the newly synthesized adenovirus DNA strands were covalently linked to an 80,000-dalton protein linked to dCMP. DNA synthesized with purified proteins was only 25-50+ the length of parental viral strands. Addition of cytosol extracts from uninfected HeLa cells to reaction mixtures containing purified proteins gave full-length adenoviral DNA strands.

Adenoviruses, Human↗
PubMed1981

Formation of a covalent complex between the 80,000-dalton adenovirus terminal protein and 5'-dCMP in vitro.

An in vitro adenovirus DNA replication system catalyzed the formation of a covalent complex between an 80,000-dalton protein and 5'-dCMP in the presence of [alpha-32P-dCTP, MgCl2, ATP, and adenovirus (Ad) DNA with a protein covalently bound to the 5' end of each strand (Ad DNA-prot). The requirement for Ad DNA-prot in this reaction was similar to that for in vitro DNA replication. When dATP, dTTP, and the 2',3'-dideoxynucleoside triphosphate (ddNTP) ddGTP were included in the reaction mixture, an elongated complex was detected, which consisted of an 80,000-dalton protein bound to a 26-base oligonucleotide. Formation of the elongated product, but not of the protein-dCMP complex, was inhibited by ddATP, ddCTP, or ddTTP. The requirements for formation of the protein-dCMP complex, the nature of the linkage between protein and dCMP, the size of the protein, and the existence of elongated forms indicated that the protein associated with the complex was identical to the 80,000-dalton Ad terminal protein found on replicating DNA molecules as described by Challberg et al. [Challberg, M. D., Desiderio, S. V. & Kelly, T. J., Jr. (1980) Proc. Natl. Acad. Sci. USA 77, 5105-5109].

Adenoviruses, Human↗
PubMed1980

Purification and characterization of a GTP-pyrophosphate exchange activity from vaccinia virions. Association of the GTP-pyrophosphate exchange activity with vaccinia mRNA guanylyltransferase . RNA (guanine-7-)methyltransferase complex (capping enzyme).

A core-associated enzyme, which catalyzes a nucleotide-pyrophosphate exchange with GTP, has been purified from vaccinia virions. The enzyme requires MgCl2 for activity, has an alkaline pH optimum, and specifically utilizes GTP as the exchanging nucleotide. The enzyme does not catalyze exchange of GMP with GTP. The GTP-PPi exchange enzyme co-purifies with vaccinia capping enzyme (RNA guanylyltransferase and RNA (guanine-7-)methyltransferase) through successive chromatography steps on DEAE-cellulose, DNA-cellulose, and phosphocellulose. GTP-PPi exchange and capping activities remain physically associated during sedimentation in a glycerol gradient. Under high salt conditions (1 M NaCl), GTP-PPi exchange, capping, and methylating activities co-sediment with an RNA triphosphatase activity and a nucleoside triphosphate phosphohydrolase activity as a 6.5 S multifunctional enzyme complex which contains two major polypeptides of 96,000 and 26,000 molecular weight. The characteristics of the various enzymatic reactions catalyzed by this complex are described. The GTP-PPi exchange reaction of vaccinia guanylyltransferase affords a simple, sensitive assay for capping enzyme function. The relevance of the GTP-PPi exchange reaction to the mechanism of transguanylylation is considered.

Cations, Divalent↗
PubMed1980

Initiation of DNA replication by the dnaG protein.

Highly purified preparations of dnaG protein from Escherichia coli prime minus strand synthesis of phage alpha 3 DNA in vitro. This protein synthesizes primer oligonucleotides which may be composed of ribonucleotide or deoxyribonucleotide moieties or both. The presence of deoxyribonucleotide moieties in the chain limits primer chain length; this effect occurs even when ribonucleoside triphosphates are included in the priming reaction. The dnaG protein can use ADP in place of ATP. Primer formation by dnaG protein is strictly stoiochiometric in vitro; one molecule of dnaG protein is required to prime one molecule of alpha 3 DNA. All of these primers are equally efficient in the subsequent elongation reaction with DNA elongation factors I and III, dnaZ gene product, and DNA polymerase III to form RFII. The site recognized by dnaG protein on alpha 3 DNA in vitro is within the same region of the alpha 3 chromosome as the origin of replication in vivo. Structural properties of this site are crucial to dnaG action in vitro. No other enzymatic activity for dnaG protein has been detected.

Bacterial Proteins↗
PubMed1980

Elongation of primed DNA templates by eukaryotic DNA polymerases.

The combined action of DNA polymerase alpha and DNA polymerase beta leads to the synthesis of full-length linear DNA strands with phi X174 DNA templates containing an RNA primer. The reaction can be carried out in two stages. In the first stage, DNA polymerase alpha catalyzes the synthesis of a chain that averaged 230 deoxynucleotides long and was covalently linked to the RNA primer. In the second stage, DNA polymerase beta elongates the DNA strand covalently attached to the RNA primer to full length. With DNA primers, DNA polymerase alpha catalyzes only limited deoxynucleotide addition whereas DNA polymerase beta alone elongates DNA primed templates to full length. DNA polymerase beta can also stimulate the synthesis of adenovirus DNA in vitro in the presence of a cytosol extract from adenovirus-infected cells. In all of these systems, dNMP incorporation catalyzed by DNA polymerase beta was sensitive to N-ethylmaleimide; however, this polymerase activity was resistant to N-ethylmaleimide with poly(rA) x (dT) as the primer template.

Adenoviruses, Human↗
PubMed1980

In vitro DNA replication of recombinant plasmid DNAs containing the origin of progeny replicative form DNA synthesis of phage phi X174.

The origin of phage phi X174 progeny replicative form (RF) DNA synthesis has been inserted into the plasmid vector pBR322 and cloned. In direct contrast to pBR322, the recombinant superhelical plasmids can substitute for phi X174 RFI DNA as template in phi X174-specific reactions in vitro. We have shown that the recombinant plasmids: (i) are cleaved by the phi X174 A protein; (ii) support net synthesis of unit-length single-stranded circular DNA in the presence of the phi X174 A protein and Escherichia coli rep protein, DNA-binding protein, and DNA polymerase III elongation system; (iii) support replication of duplexes catalyzed by the phi X174 A protein and extracts of E. coli.

Bacterial Proteins↗
PubMed1979

5'-Hydroxyl polyribonucleotide kinase from HeLa cell nuclei. Purification and properties.

An enzyme, 5'-hydroxyl polyribonucleotide kinase, which catalyzes the phosphorylation of 5'-hydroxyl ends of RNA in the presence of ATP, has been isolated from extracts of HeLa cell nuclei. The kinase requires a divalent cation (Mg2+ or Mn2+) for activity, has an alkaline pH optimum, and is sensitive to the sulfhydryl antagonist N-ethylmaleimide. 5'-hydroxyl terminated polydeoxyribonucleotides are phosphorylated much less efficiently than the 5'-hydroxyl terminated polyribonucleotides, and the kinase preparation is inactive on ribonucleoside 3'-monophosphates. Enzyme activity is inhibited by ADP and by pyrophosphate. The sedimentation coefficient of the kinase is estimated to be 5.6 S from glycerol gradient centrifugation.

Cations, Divalent↗
PubMed1979

Role of polymeric forms of the bacteriophage phi X174 coded gene A protein in phi XRFI DNA cleavage.

Gene A of the phi X174 genome codes for two proteins, A and A* (Linney, E.A., and Hayashi, M.N. (1973) Nature New Biol. 245, 6-8) of molecular weights 60,000 and 35,000, respectively. The phi X A* protein is formed from a natural internal initiator site within the A gene cistron while the phi X A protein is the product of the entire A gene. These two proteins have been purified to homogeneity as judged by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Previous studies have shown that the phi X A protein is an endonuclease which specifically introduces a discontinuity in the A cistron of the viral strand of supertwisted phi XRFI DNA. In addition to this activity, the phi X A protein also causes relaxation of supertwisted phi XRFI DNA and formation of a phi XRFH DNA . phi X A protein complex which has a discontinuity in the A cistron of the viral strand. This isolatable complex supports DNA synthesis when supplemented with extracts of uninfected Escherichia coli which lack phi X A protein and phi XRFI DNA. The phi XRFII DNA . phi X A protein complex can be attacked by exonuclease III but is not susceptible to attack by E. coli DNA polymerase I, indicating that the 5'-end of the complex is blocked. Attempts to seal the RFII structure generated from the phi XRFII DNA . phi X A protein complex with T4 DNA ligase in the presence or absence of DNA polymerase were unsuccessful. The phi X A protein does not act catalytically in the cleavage of phi XRFI DNA. Under conditions leading to the quantitative cleavage of phi XRFI DNA, the molar ratio of phi XRFI DNA to added phi X A protein was approximately 1:10. At this molar ratio, cross-linking experiments with dimethyl suberimidate yielded 10 distinct protein bands which were multiples of the monomeric phi X A protein. In the absence of DNA or in the presence of inactive DNA (phi XRFII DNA) no distinct protein bands above a trimer were detected. We found it possible in vitro to form a phi XRFII DNA . phi X A protein complex with wild-type phi XRFI DNA (phi X A gene+) and with phi XRFI DNA isolated from E. coli (su+) infected with phage phi X H90 (an am mutant in the phi X A gene). Thus, in vitro, in contrast to in vivo studies, phi X A protein is not a cis acting protein. The purified phi X A* protein does not substitute for the phi X A protein in in vitro replication of phi XRFI DNA nor does it interfere with the action of the phi X A protein which binds only to supertwisted phi XRFI DNA. In contrast, the phi X A* protein binds to all duplex DNA preparations tested. This property prevents nucleases of E. coli from hydrolyzing duplex DNAs to small molecular weight products.

Bacteriophage phi X 174↗
PubMed1979

Complementation of the temperature-sensitive defect in H5ts125 adenovirus DNA replication in vitro.

Soluble extracts of adenovirus-infected HeLa cell nuclei support DNA replication on exogenous adenovirus DNA templates. Conditions of synthesis using both wild-type and temperature-sensitive extracts have been defined. Nuclear extracts prepared from cells permissively infected with the adenovirus mutant H5ts125 expressed the temperature-sensitive phenotype and could be inactivated at 37 degrees C in vitro. These extracts were completely complemented by the addition of wild-type adenovirus DNA binding protein but not by H5ts125 DNA binding protein. Enhancement by binding protein in the mutant extracts represents replication, as demonstrated by the production of full-sized products and orderly chain elongation originating, as in vivo, at both ends of the linear DNA. Replicative synthesis required the 5'-terminal protein bound covalently to template DNA and could be inhibited by denaturation of this 55,000-dalton protein. Various inhibitors of eukaryotic DNA polymerases, such as aphidicolin and 2',3'-dideoxythymidine triphosphate, inhibited replication of exogenous adenovirus templates in this system as they do in previously reported systems that only elongate endogenous replicating intermediates.

Adenoviruses, Human↗
PubMed1979

Analysis of in vitro replication of different DNAs.

The conversion of single-stranded circular DNA to duplex DNA in vitro occurs by at least three different mechanisms. These differences reside in the manner of priming of these DNAs. In contrast, the elongation of primed DNA templates is a general reaction. A number of these proteins have been isolated and further characterized. In addition, cell-free preparations capable of supporting phi X RFI DNA replication as well as the synthesis of progeny viral phi X174 single-stranded circular DNA have been prepared.

Coliphages↗
PubMed1978

Purification of mRNA guanylyltransferase from vaccinia virions.

GTP:RNA guanylyltransferase, the enzyme which catalyzes the guanylylation of the 5' termini of viral mRNAs, has been isolated and purified approximately 10,000-fold from cores of vaccinia virus. S-adenosyl-methionine:mRNA (guanine-7)-methyltransferase copurified with guanylyltransferase activity through chromatography on DNA agarose, phosphocellulose, and centrifugation in glycerol gradients, suggesting that the two activities are closely associated. The molecular weight of native guanylyltransferase- and 7-methyltransferase-associated activities was approximately 120,000 as determined by glycerol gradient centrifugation. Guanylytransferase purified by electrophoresis on polyacrylamide gels at pH 4.5 lacked 7-methyltransferase activity. Analysis by electrophoresis on sodium dodecyl sulfate-polyacrylamide gels of electrophoretically purified native guanylyltransferase showed the presence of one major band of polypeptide which had a molecular weight of approximately 59,000.

Guanine Nucleotides↗