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At least 127 records · Page 7Linked to original sources
PubMed1992

Selective inhibition of the 3'-to-5' exonuclease activity associated with Epstein-Barr virus DNA polymerase by ribonucleoside 5'-monophosphates.

Epstein-Barr virus (EBV) DNA polymerase possesses a proofreading 3'-to-5' exonuclease activity (Tsurumi, T. (1991) Virology 182, 376-381). The 3'-to-5' exonuclease activity can be selectively inhibited by ribonucleoside 5'-monophosphates, while no inhibition of the DNA polymerase activity can be observed even when the template/primer concentrations are rate-limiting. Deoxynucleoside monophosphates except 5'dGMP have almost no effect on the exonuclease activity. Of the four ribonucleoside monophosphates, 5'GMP is the most potent (62% inhibition at 5 mM). The kinetic study shows that 5'-GMP inhibits the exonuclease activity competitively with respect to DNA template/primer. During DNA polymerization process the EBV DNA polymerase catalyzes the DNA-dependent conversion of complementary deoxynucleoside triphosphate to monophosphate form. With poly(dT).oligo(rA) as a template primer, selective inhibition of the exonuclease activity by 5'-GMP results in a decrease in the amount of free dAMP generated which is complementary to the template DNA, suggesting the functional relationship between the editing exonuclease activity and the chain elongation activity of the EBV DNA polymerase molecule.

Escherichia coli↗
PubMed2003

Substrate specificity and phosphorylation of antiviral and anticancer nucleoside analogues by human deoxyribonucleoside kinases and ribonucleoside kinases.

Structural analogues of nucleosides, nucleoside analogues (NA), are used in the treatment of cancer and viral infections. Antiviral NAs inhibit replication of the viral genome, whereas anticancer NAs inhibit cellular DNA replication and repair. NAs are inactive prodrugs that are dependent on intracellular phosphorylation to their pharmacologically active triphosphate form. The deoxyribonucleoside kinases (dNK) and ribonucleoside kinases (rNK) catalyze the first phosphorylation step, converting deoxyribonucleosides and ribonucleosides to their corresponding monophosphate form. The dNKs have been studied intensively, whereas the rNKs have not been as thoroughly investigated. This overview is focused on the substrate specificity, tissue distribution, and subcellular location of the mammalian dNKs and rNKs and their role in the activation of NAs.

Amino Acid Sequence↗
PubMed1980

Mechanism of inhibition of deoxyribonucleic acid synthesis by 1-beta-D-arabinofuranosyladenosine triphosphate and its potentiation by 6-mercaptopurine ribonucleoside 5'-monophosphate.

The mechanism of inhibition of DNA synthesis by 1-beta-D-arabinofuranosyl-ATP (ara-ATP) and the potentiation of this inhibition by 6-mercaptopurine ribonucleoside 5'-monophosphate (6-MPR-P) have been investigated with mammalian DNA polymerase delty by using poly(dA-dT) as the template. The inhibition of DNA synthesis by ara-ATP correlates with incorporation of ara-AMP into poly(dA-dT). Nearest-neighbor analysis indicates that ara-AMP does not act as an absolute chain terminator but rather that chains with 3'-terminal arabinosyl nucleotides are extended slowly. The inhibition of DNA synthesis by ara-ATP is markedly enhanced by the addition of the nucleotide derivative of 6-mercaptopurine, 6-mercaptopurine ribonucleoside 5'-monophosphate. The increased inhibition of DNA synthesis in the presence of 6-MPR-P is due to increased incorporation of ara-AMP. The mechanism by which 6-MPR-P increases the incorporation of ara-AMP is by selective inhibition of the 3' to 5' exonuclease activity of DNA polymerase, thereby preventing the removal of newly incorporated ara-AMP at 3' termini of DNA chains.

Adenosine Triphosphate↗
PubMed2003

Epimerization at carbon-5' of (5'R)-[5'-2H]adenosylcobalamin by ribonucleoside triphosphate reductase: cysteine 408-independent cleavage of the Co-C5' bond.

The adenosylcobalamin-dependent ribonucleoside triphosphate reductase (RTPR) from Lactobacillus leichmannii catalyzes the reduction of ribonucleoside triphosphates to deoxyribonucleoside triphosphates. RTPR also catalyzes the exchange of the C5'-hydrogens of adenosylcobalalamin with solvent hydrogen. A thiyl radical located on Cys 408 is generated by reaction of adenosylcobalamin at the active site and is proposed to be the intermediate for both the nucleotide reduction and the 5'-hydrogen exchange reactions. In the present research, a stereochemical approach is used to study the mechanism of the Co-C5' bond cleavage of adenosylcobalamin in the reaction of RTPR. When stereoselectively deuterated coenzyme, (5'R)-[5'-(2)H(1)] adenosylcobalamin (5'R/S = 3:1), was incubated with RTPR or the Cys 408 viariants, C408A-RTPR and C408S-RTPR in the presence of dGTP, the deuterium at the 5'-carbon was stereochemically scrambled, leading to epimerization of the (5'S)-[5'-(2)H(1)]- and (5'R)-[5'-(2)H(1)]-isotopomers. Observation of epimerization with mutated RTPR proves that transient cleavage of the Co-C5' bond occurs in the absence of the thiol group on Cys 408. The rate constants for epimerization by RTPR, C408A-RTPR, and C408S-RTPRs in the presence of dGTP are 5.1, 0.28, and 0.42 s(-1), respectively. Only the wild-type RTPR catalyzes the 5'-hydrogen exchange reaction. Both epimerization and 5'-hydrogen exchange reactions are stimulated by the allosteric effector dGTP, and epimerization is not detected in the absence of the effector. Mechanistic implications with respect to wt-RTPR-mediated carbon cobalt bond homolysis and the intermediacy of the 5'-deoxyadenosyl radical will be presented.

Cobalt↗
PubMed1998

Nucleic Acid Related Compounds. 105. Synthesis of 2',3'-Didehydro-2',3'-dideoxynucleosides from Ribonucleoside Cyclic 2',3'-(Sulfates or Phosphates) or 2',3'-Dimesylates via Reductive Elimination with Sodium Naphthalenide(1).

Treatment of purine ribonucleosides with thionyl fluoride resulted in formation of cyclic 2',3'-sulfite esters. Acetylation of the 5'-hydroxy group and Sharpless oxidation (NaIO(4)/RuCl(3)) gave the cyclic 2',3'-sulfate ester derivatives. Treatment of 5'-O-silyl-protected ribonucleosides with thionyl chloride followed by oxidation gave an alternative route to the cyclic 2',3'-sulfates. Reductive elimination with sodium naphthalenide (THF/-50 degrees C) gave the 2',3'-unsaturated nucleosides. Parallel treatment of adenosine cyclic 2',3'-phosphate gave the 2',3'-olefin. The adenine, hypoxanthine, and 2-amino-6-methoxypurine 2',3'-didehydro-2',3'-dideoxynucleosides were prepared efficiently (40-60% overall yields of crystalline, analytically pure products; 3-5 steps, some combined into one-flask procedures) by treatment of 5'-O-protected 2',3'-di-O-mesylribonucleosides with sodium naphthalenide. Reactions were performed at or below ambient temperature with readily available reagents and standard laboratory conditions.

Journal Article↗
PubMed2000

The broad-spectrum antiviral ribonucleoside ribavirin is an RNA virus mutagen.

The ribonucleoside analog ribavirin (1-beta-D-ribofuranosyl-1,2, 4-triazole-3-carboxamide) shows antiviral activity against a variety of RNA viruses and is used in combination with interferon-alpha to treat hepatitis C virus infection. Here we show in vitro use of ribavirin triphosphate by a model viral RNA polymerase, poliovirus 3Dpol. Ribavirin incorporation is mutagenic, as it templates incorporation of cytidine and uridine with equal efficiency. Ribavirin reduces infectious poliovirus production to as little as 0. 00001% in cell culture. The antiviral activity of ribavirin correlates directly with its mutagenic activity. These data indicate that ribavirin forces the virus into 'error catastrophe'. Thus, mutagenic ribonucleosides may represent an important class of anti-RNA virus agents.

Antiviral Agents↗
PubMed1988

Nonenzymatic synthesis of 5-aminoimidazole ribonucleoside and recognition of its facile rearrangement.

5-Amino-1-beta-D-ribofuranosylimidazole 5'-monophosphate (AIR, 1) is the ubiquitous precursor to the purine ribonucleotides in vivo, and it serves as the biochemical precursor to the pyrimidine portion of thiamin (vitamin B1) in certain prokaryotic organisms. The corresponding ribonucleoside (AIRs, 5b) was prepared via chemical (nonenzymatic) synthesis from 5-amino-1-beta-D-ribofuranosylimidazole-4-carboxamide. The tri-O-acetylated derivative of AIRs (5a) was also prepared, and it was shown to undergo a facile ring transformation in aqueous pH 7 buffer to afford N-(imidazol-4-yl)-2,3,5-tri-O-acetyl-D-ribofuranosylamine as a 1:2 mixture of alpha and beta anomers (6a). Under similar conditions, compound 5b affords the corresponding unprotected beta-ribonucleosides 6b. This Dimroth-type ring transformation reaction of 5 to 6, which occurs primarily in neutral aqueous solution, may be responsible for the previously reported lability of AIRs and its derivatives. It may also have relevance to the postulated early biotic pathway to the 9- and 3-substituted purine nucleotide components of an all-purine biopolymer.

Acetylation↗
PubMed1990

The anaerobic ribonucleoside triphosphate reductase from Escherichia coli requires S-adenosylmethionine as a cofactor.

Extracts from anaerobically grown Escherichia coli contain an oxygen-sensitive activity that reduces CTP to dCTP in the presence of NADPH, dithiothreitol, Mg2+ ions, and ATP, different from the aerobic ribonucleoside diphosphate reductase (2'-deoxyribonucleoside-diphosphate: oxidized-thioredoxin 2'-oxidoreductase, EC 1.17.4.1) present in aerobically grown E. coli. After fractionation, the activity required at least five components, two heat-labile protein fractions and several low molecular weight fractions. One protein fraction, suggested to represent the actual ribonucleoside triphosphate reductase was purified extensively and on denaturing gel electrophoresis gave rise to several defined protein bands, all of which were stained by a polyclonal antibody against one of the two subunits (protein B1) of the aerobic reductase but not by monoclonal anti-B1 antibodies. Peptide mapping and sequence analyses revealed partly common structures between two types of protein bands but also suggested the presence of an additional component. Obviously, the preparations are heterogeneous and the structure of the reductase is not yet established. The second, crude protein fraction is believed to contain several ancillary enzymes required for the reaction. One of the low molecular weight components is S-adenosylmethionine; a second component is a loosely bound metal. We propose that S-adenosylmethionine together with a metal participates in the generation of the radical required for the reduction of carbon 2' of the ribosyl moiety of CTP.

Anaerobiosis↗
PubMed2006

A novel nucleotide found in human erythrocytes, 4-pyridone-3-carboxamide-1-beta-D-ribonucleoside triphosphate.

We report the identification of a hitherto unknown nucleotide that is present in micromolar concentrations in the erythrocytes of healthy subjects and accumulates at levels comparable with the ATP concentration in erythrocytes of patients with chronic renal failure. The unknown nucleotide was isolated and identified by liquid chromatography with UV and tandem mass detection, (1)H nuclear magnetic resonance and infrared spectroscopy as 4-pyridone-3-carboxamide-1-beta-D-ribonucleoside triphosphate (4PYTP), a structure indicating association with metabolism of the oxidized nicotinamide compounds. Subsequently, we demonstrated formation of 4PYTP in intact human erythrocytes during incubation with the chemically synthesized nucleoside precursor 4-pyridone-3-carboxamide-1-beta-D-ribonucleoside (4PYR). We noted preferential accumulation of monophosphate of 4PYR (4PYMP) over 4PYTP as well as a decrease in erythrocyte ATP concentration during incubation with 4PYR. Both the 4PYR phosphorylation and ATP depletion were blocked by an inhibitor of adenosine kinase. Plasma concentration of 4PYR was detectable but very low (0.013 +/- 0.006 microm) in contrast with the high daily urine excretion of this compound (26.7 +/- 18.2 micromol/24 h) in healthy subjects, indicating much greater renal clearance than other nicotinamide metabolites, nucleosides, or creatinine. We also noted a 40-fold increase in 4PYR plasma concentration in patients with chronic renal failure (0.563 +/- 0.321 microm). We suggest that 4PYTP formation in the erythrocytes is a hitherto unknown process aimed at sequestering potentially toxic 4PYR in a form that could be safely transported and subsequently released and excreted during passage of erythrocytes through the kidney.

Adenosine Kinase↗
PubMed1999

Adenosylcobalamin-dependent ribonucleoside triphosphate reductase from Lactobacillus leichmannii. Rapid, improved purification involving dGTP-based affinity chromatography plus biophysical characterization studies demonstrating enhanced, "crystallographic level" purity.

Ribonucleoside triphosphate reductase (RTPR, EC 1.17.4.2) from Lactobacillus leichmannii is a 5'-deoxyadenosylcobalamin-dependent (AdoCbl; Coenzyme B12) enzyme. RTPR is also a prototypical adenosylcobalamin-dependent ribonucleotide reductase, one that, as its name indicates, converts ribonucleoside triphosphates (NTP) to deoxyribonucleoside triphosphates (dNTP). Upon substrate binding to RTPR, AdoCbl's cobalt-carbon bond is cleaved to generate cob(II)alamin, 5'-deoxyadenosine, and the cysteine (C408) derived thiyl radical. Five key cysteines (Cys 119, 408, 419, 731, and 736), from among the ten total cysteines, are involved in RTPR's catalytic mechanism. A critical examination of the RTPR isolation and purification literature suggested that the purification protocol currently used results in RTPR which contains 2040% microheterogeneity, along with minor contamination by other proteins. In addition, no report of crystalline RTPR has ever appeared. The literature indicates that irreversible cysteine oxidation (e.g., to -SO2H or -SO3H) is one highly plausible reason for the microheterogeneity of RTPR. The literature also indicates that improvement in the level of enzyme purity is the most effective next step in coaxing enzymes to crystallize that have previously failed to do so. A shortened, improved purification of RTPR has been developed, one involving a shorter purification time, a lower pH, a higher concentration of the more effective reductant DTT (all designed to help protect the cysteines from oxidation), and a final step utilizing our recently reported, improved dGTP-based affinity chromatography resin. The resultant RTPR is approximately 20-30% higher in both specific activity and in its ability to undergo single turnovers, and is homogeneous by mass spectrometry and dynamic light scattering. Additionally, the revised purification procedure eliminates > 30 proteins present in 2-3% amounts along with damaged RTPR that does not bind properly (i.e. tightly) to the dGTP-affinity resin. Finally, dGTP-based affinity chromatography purified RTPR has yielded the first reported, albeit small, single crystals of RTPR.

Allosteric Regulation↗
PubMed1996

Solid support synthesis of all-Rp-oligo(ribonucleoside phosphorothioate)s.

The first method for solid support synthesis of all-Rp-oligo(ribonucleoside phosphorothioate)s is presented as well as attempts to increase the stereoselectivity of the key step in this approach. The synthetic strategy consists of (i) a solid support synthesis procedure, using 5'-O-(4-methoxytriphenylmethyl)-2'-O-tert-butyldimethylsilyl-ri bon ucleoside 3'-H- phosphonates, that due to stereoselectivity in the condensation step, gives oligomers with mostly Sp-H-phosphonate diesters (72-89% under standard conditions), (ii) stereospecific sulfurization with S8 in pyridine to produce oligo(ribonucleoside phosphorothioate)s enriched with internucleosidic linkages of Rp configuration, (iii) treatment of the deprotected oligonucleotides with the enzyme Nuclease P1 from Penicillium citrinum, that specifically catalyses cleavage of Sp-phosphorothioate diester linkages, which leaves a mixture of oligomers having all internucleosidic linkages as Rp-phosphorothioates, and finally (iv) isolation and HPLC purification of the full length all-Rp oligomer. Mixed sequences containing the four common nucleosidic residues up to the chain length of a heptamer were synthesized. Change of N-4-protection on the cytidine building block from propionyl to N-methylpyrrolidin-2-ylidene gave a slightly improved diastereoselectivity in H-phosphonate diester formation. Increased selectivity up to 99+% was obtained with the guanosine building block when the amount of pyridine in the coupling step was reduced.

Chromatography, High Pressure Liquid↗
PubMed2006

Genes encoding ribonucleoside hydrolase 1 and 2 from Corynebacterium ammoniagenes.

Two kinds of nucleoside hydrolases (NHs) encoded by rih1 and rih2 were cloned from Corynebacterium ammoniagenes using deoD- and gsk-defective Escherichia coli. Sequence analysis revealed that NH 1 was a protein of 337 aa with a deduced molecular mass of 35,892 Da, whereas NH 2 consisted of 308 aa with a calculated molecular mass of 32 310 Da. Experiments with crude extracts of IPTG-induced E. coli CGSC 6885(pTNU23) and 6885(pTNI12) indicated that the Rih1 enzyme could catalyse the hydrolysis of uridine and cytidine and showed pyrimidine-specific ribonucleoside hydrolase activity. Rih2 was able to hydrolyse both purine and pyrimidine ribonucleosides with the following order of activity -- inosine>adenosine>uridine>guanosine>xanthosine>cytidine -- and was classified in the non-specific NHs family. rih1 and rih2 deletion mutants displayed a decrease in cell growth on minimal medium supplemented with pyrimidine and purine/pyrimidine nucleosides, respectively, compared with the wild-type strain. Growth of each mutant was substantially complemented by introducing rih1 and rih2, respectively. Furthermore, disruption of both rih1 and rih2 led to the inability of the mutant to utilize purine and pyrimidine nucleosides as sole carbon source on minimal medium. These results indicated that rih1 and rih2 play major roles in the salvage pathways of nucleosides in this micro-organism.

Amino Acid Sequence↗
PubMed1995

5-aminoimidazole-4-carboxamide ribonucleoside. A specific method for activating AMP-activated protein kinase in intact cells?

The AMP-activated protein kinase (AMPK) is believed to protect cells against environmental stress (e.g. heat shock) by switching off biosynthetic pathways, the key signal being elevation of AMP. Identification of novel targets for the kinase cascade would be facilitated by development of a specific agent for activating the kinase in intact cells. Incubation of rat hepatocytes with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) results in accumulation of the monophosphorylated derivative (5-aminoimidazole-4-carboxamide ribonucleoside; ZMP) within the cell. ZMP mimics both activating effects of AMP on AMPK, i.e. direct allosteric activation and promotion of phosphorylation by AMPK kinase. Unlike existing methods for activating AMPK in intact cells (e.g. fructose, heat shock), AICAR does not perturb the cellular contents of ATP, ADP or AMP. Incubation of hepatocytes with AICAR activates AMPK due to increased phosphorylation, causes phosphorylation and inactivation of a known target for AMPK (3-hydroxy-3-methylglutaryl-CoA reductase), and almost total cessation of two of the known target pathways, i.e. fatty acid and sterol synthesis. Incubation of isolated adipocytes with AICAR antagonizes isoprenaline-induced lipolysis. This provides direct evidence that the inhibition by AMPK of activation of hormone-sensitive lipase by cyclic-AMP-dependent protein kinase, previously demonstrated in cell-free assays, also operates in intact cells. AICAR should be a useful tool for identifying new target pathways and processes regulated by the protein kinase cascade.

AMP-Activated Protein Kinases↗
PubMed1970

Effects of ribonucleosides on thymidine incorporation: selective reversal of the inhibition of deoxyribonucleic acid synthesis in thymineless auxotrophs of Escherichia coli.

Addition of certain ribonucleosides to exponentially growing cultures of Escherichia coli increased the extent of thymidine incorporation. The prolonged uptake of thymidine was correlative with the ability of these ribonucleosides to prevent the degradation of thymidine. In addition to protecting thymidine, uridine reversed partially (70 to 80%) the inhibition of deoxyribonucleic acid (DNA) synthesis in thymineless auxotrophs by cytosine arabinoside, hydroxyurea, and nalidixic acid. This reversal was selective for auxotrophic strains since no reversal of inhibition by uridine was observed in any of the prototrophic strains examined. In the presence of uridine, the rapid assimilation of thymidine by prototrophic and auxotrophic strains was prevented and the rate of DNA synthesis became a function of the available exogenous thymidine. Under these conditions, prototrophic strains accumulated equivalent amounts of thymidine into the acid-soluble (pool) and acid-insoluble (DNA) cell fractions. In contrast, 95 to 98% of the thymidine taken up by auxotrophs was found in the acid-insoluble (DNA) cell fraction. The results suggest that different mechanisms for DNA synthesis exist in auxotrophs and prototrophs. Based on these observed differences, some possible mechanisms for the selective reversal of the inhibition of DNA synthesis in auxotrophs are discussed.

Carbon Isotopes↗
PubMed2006

Hydrolytic approach for production of deoxyribonucleoside- and ribonucleoside-5 -monophosphates and enzymatic synthesis of their polyphosphates.

A new, simple, and ingenious method for enzymatic synthesis of deoxy- and ribonucleoside-5 -triphosphates (dNTP and NTP, respectively) has been developed. The method includes the following stages: hydrolysis of DNA with DNase and immobilized S1-nuclease, phosphorylation of the resulting deoxy- and ribonucleoside-5 -monophosphates (dNMP and NMP, respectively) with nucleotidyl kinase from Escherichia coli, and purification by chromatography of the synthesized dNTP and NTP. dNMP was phosphorylated using an ATP-regenerating system based on acetokinase from E. coli and lithium acetylphosphate.

Acetate Kinase↗
PubMed1985

Regulation of a ribonucleoside reductase during the early generative phase in Acetabularia.

The activity of a ribonucleoside reductase was estimated during the life cycle of Acetabularia. During the early generative phase the enzyme activity was dramatically increased. Regulation of the ribonucleoside reductase was observed even in the absence of the nucleus. The increase in activity was inhibited by chloramphenicol but not by cycloheximide. These results indicate that the enzyme is translated on 70 S ribosomes.

Acetabularia↗
PubMed1990

Demonstration of binding components specific for 7,8-disubstituted guanine ribonucleosides in murine B lymphocytes.

7,8-Disubstituted guanine ribonucleosides are known to be potent intracellular modulators of immune responses. These compounds trigger and modulate a wide variety of lymphocyte responses including effects exerted directly on B cells. However, little is known about their mechanism of action. The current paper describes studies undertaken to evaluate whether binding components specific for these bioactive molecules exist in splenic B lymphocytes. After exposure of cells to labeled nucleoside, two different pools of nucleoside can be distinguished: a rapidly exchangeable nucleoside pool and a slowly exchangeable pool. The material in the latter pool consists of authentic unaltered nucleoside that is complexed to a relatively hydrophobic cellular component with an apparent Mr of 30,000-40,000; binding appears to interfere with free interaction of the nucleoside's cis hydroxyls with a boronate affinity resin. The slowly exchangeable nucleoside pool is seen to localize predominantly to the nucleus in electron microscopic autoradiographs. This pool is maximally bound by 30 min of incubation. Specific, saturable binding is demonstrable, with an apparent Kd of approximately 7 microM. This value correlates well with concentrations at which half-maximal biological activity occurs and suggests that the binding component likely mediates antigen-dependent immunomodulatory activity. Splenic B cells express approximately 2 x 10(4) binding sites/cell, whereas thymic lymphocytes, which do not respond functionally to nucleosides, do not display a measurable number of nucleoside binding sites. Ligand specificity of the binding interaction is confirmed by binding inhibition studies, in which binding inhibitory activity of unlabeled agonistic structural analogs recapitulate their degree of immunobiological activity. These data are most consistent with the existence of a saturable binding component with apparent specificity for 7,8-disubstituted guanine ribonucleosides in splenic B cells.

Animals↗
PubMed1989

Affinity labeling of the active center and ribonucleoside triphosphate binding site of yeast DNA primase.

A highly selective affinity labeling procedure has been applied to map the active center of DNA primase from the yeast Saccharomyces cerevisiae. Enzyme molecules that have been modified by covalent attachment of benzaldehyde derivatives of adenine nucleotides are autocatalytically labeled by incubation with a radioactive ribonucleoside triphosphate. The affinity labeling of primase requires a template DNA, is not affected by DNase and RNase treatments, but is sensitive to proteinase K. Both the p58 and p48 subunits of yeast DNA primase appear to participate in the formation of the catalytic site of the enzyme, although UV-photocross-linking with [alpha-32P]ATP locates the ribonucleoside triphosphate binding site exclusively on the p48 polypeptide. The fixation of the radioactive product has been carried out also after the enzymatic reaction. Under this condition the RNA primers synthesized by the DNA polymerase-primase complex under uncoupled DNA synthesis conditions are linked to both DNA primase and DNA polymerase. When DNA synthesis is allowed to proceed first, the labeled RNA chains are fixed exclusively to the DNA polymerase polypeptide. These results, in accord with previous data, have been used to propose a model illustrating the interactions and the putative roles of the polypeptides of the DNA polymerase-primase complex.

Adenosine Triphosphate↗