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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The replication in Bacillus subtilis of the staphylococcal R plasmids pE194, pBD15, pUB110, pSA0501, and pSA2100 has been studied in the presence of hydroxyurea. In all cases, an enrichment for covalently closed circular DNA compared with chromosomal DNA was observed. In this respect, hydroxyurea mimics the effect previously observed with pUB110, using strains carrying the conditional mutation dnaA13. This mutation has been reported to affect ribonucleotide reductase (G. W. Bazill and D. Karamata, Mol. Gen. Genet. 117:19-29, 1972). An explanation for these effects is offered, together with some supporting evidence.
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PMID:Differential effect of hydroxyurea on the replication of plasmid and chromosomal DNA in Bacillus subtilis. 10 36

The development of bacteriophages SPP1 and phi 29 has been studied in several B. sutilis mutants defective in host DNA replication, under non permissive conditions. Several gene products, involved in the synthesis of host DNA, are required for phi 29 replication, while SPP1 seems to require only the host DNA polymerase III. In addition both phages are unable to grow in a dna A mutant (ribonucleotide reductase). Taking advantage of the fact that SPP1 DNA is actively replicated in several dna mutants at non-permissive temperature, we have studied the structure of the replicative intermediates of this phage in the absence of interfering host DNA synthesis. Fast sedimenting forms of SPP1 DNA can be isolated from phage infected cells and evidence of covalently joined concatemers has been obtained, suggesting the presence of terminally repeated sequences.
Mol Gen Genet 1978 Nov 29
PMID:SPP1 DNA replicative forms: growth of phage SPP1 in Bacillus subtilis mutants temperature-sensitive in DNA synthesis. 10 41

The biological pathways of ribonucleotide reduction are briefly reviewed. The hypothesis is presented that reduction of ribonucleoside triphosphates to their deoxynucleotide analogs through the mediation of vitamin B12 or a similar corrinoid preceded and was necessary for the subsequent development of a DNA-type genome. There are two known biological systems for ribonucleotide reduction: (1) The ribonucleoside diphosphate reduction system which utilizes a nonheme iron ribonucleotide reductase enzyme, thioredoxin and its reductase, and NADPH. This enzyme complex is found in most bacteria, some higher organisms, and in all animals. (2) The ribonucleoside triphosphate reduction system which utilizes adenosyl cobalamin, ribonucleotide reductase and either thioredoxin or a disulfhydryl compound. The cobalamin-dependent reductase is restricted to a few species of bacteria and blue-gree algae. This system is considered more primitive than the iron reductase one based on their differences in distribution, components, and products.
J Mol Evol 1977 Dec 29
PMID:Ribonucleotide reduction and the possible role of cobalamin in evolution. 59 75

The expression of the genes encoding ribonucleotide reductase in Escherichia coli was investigated in cultures synchronized by obtaining the smallest cells in a population after sucrose gradient centrifugation. Specific activity of ribonucleotide reductase and DNA initiation were found to increase in parallel, periodically as a function of the cell cycle. The expression of nrd was also determined in cells synchronized by periodic repeated doubling in a phosphate limited medium. Antibodies directed against the B2 subunit of ribonucleotide reductase were raised in a rabbit and purified. Immunoprecipitation of the B2 subunit and RNA-DNA dot blot hybridization assays were developed and employed to determine the expression of ribonucleotide reductase translational and transcriptional products during the cell cycle. Both of nrd-mRNA and B2 subunit expression were found to increase each generation at approximately the same time DNA synthesis was initiated and then to decrease back to the basal level shortly after DNA initiation. These results provided evidence of cell cycle dependent regulation of ribonucleotide reductase in E. coli. When the upstream regulatory region of nrd was fused to a promoterless lacZ gene on a single copy plasmid, lac-mRNA and beta-galactosidase were found to be synthesized in parallel to nrd expression from the chromosomal operon. When nrd sequences surrounding the promoter were removed from this construct, lac-mRNA and beta-galactosidase synthesis were no longer cell cycle regulated.
Mol Biol Cell 1992 Oct
PMID:Escherichia coli ribonucleotide reductase expression is cell cycle regulated. 138 14

New cellular traits of Cockayne's syndrome (CS) associated with DNA precursor metabolism have been identified, namely, hypersensitivity to the toxicity of low concentrations of deoxyguanosine (dG) and abnormal changes in deoxyribonucleotide (dNTP) pools in response to dG or UV. dG treatment results in similar ribonucleotide pool changes in wild-type and CS cells, i.e., GTP levels increase at least twofold. However, the changes in the pool size of the purine deoxyribonucleotides are significantly different; in wild-type cells dATP and dGTP pools increase threefold, but remain unchanged in CS. The mechanism by which dG kills CS cells is not clear, but unlike the inherited purine nucleoside phosphorylase deficiency disease, the toxicity of dG is not due to the accumulation of dGTP and the consequent feedback inhibition of ribonucleotide reductase. UV induces different dNTP pool changes in CS and wild-type cells. In wild-type cells dTTP, dCTP, and dATP pools increase three- to fivefold within 4 h of irradiation, while the dGTP pool contracts. In CS cells, only the dGTP pool expands (four- to sixfold), while the other three contract. Each of these new phenotypic traits, together with UV sensitivity, is coordinately corrected in the complementing proliferating CSA x CSB hybrid cells.
Somat Cell Mol Genet 1992 Sep
PMID:Cockayne's syndrome fibroblasts are characterized by hypersensitivity to deoxyguanosine and abnormal DNA precursor pool metabolism in response to deoxyguanosine or ultraviolet light. 147 5

The enzymes of DNA polymerization and DNA precursor synthesis are assembled in the replitase complex during the S phase of the cell cycle. Cross-inhibition is a phenomenon shown by enzymes of the replitase complex, in which inhibition of one enzyme of the complex leads to inhibition of a second, unrelated enzyme. This inhibition occurs only in vivo and only during S phase. The second enzyme shows no inhibition in vitro. In this study, using Chinese hamster embryo fibroblast cells, we have shown that direct allosteric interactions, i.e., structural interaction from a remote site within the replitase complex, is the cause of cross-inhibition of thymidylate synthase activity by the inhibitors of ribonucleotide reductase and DNA polymerase, because disruptions of the deoxynucleotide pools, which would be predicted for alternative explantations, do not occur. Cross-inhibition of DNA polymerase by hydroxyurea is demonstrated by the cessation of DNA synthesis when ribonucleotide reductase block is circumvented by the provision of all four deoxynucleosides. In addition to the cross-inhibition for thymidylate synthase and DNA polymerase, we have also presented evidence, on the basis of alterations of the in vivo conversion of deoxyuridine to dUMP, that cross-inhibition also occurs for the enzyme thymidine kinase. This conclusion is further supported by the lack of inhibition of the similar process in RNA synthesis, because enzymes of RNA synthesis are not included in the replitase complex. To facilitate the measurements, we have introduced a novel method of distinguishing between thymidine and deoxyuridine derivatives, making use of the fact that a tritium label placed in the 5'-position of deoxyuridine is removed on conversion to thymidine by methylation, whereas a tritium placed in the 6'-position is not.
Mol Pharmacol 1990 Jul
PMID:Allosteric interaction of components of the replitase complex is responsible for enzyme cross-inhibition. 169 15

Deoxyribonucleotide pool imbalances are frequently mutagenic. We have studied two Chinese hamster ovary cell lines, Thy- 49 and Thy- 303, that were originally characterized by M. Meuth (Mol. Cell. Biol. 1:652-660, 1981). In comparison with wild-type CHO cells, both lines have elevated dCTP/dTTP ratios, resulting from loss of feedback control of CTP synthetase. While asynchronous cultures of both cell lines contain nearly identical deoxyribonucleoside triphosphate (dNTP) pools and both display elevated spontaneous mutation frequencies, the mutation frequencies between the two cell lines differ by as much as 10-fold. We asked whether differences in dNTP pools could be seen in extracts of rapidly isolated nuclei. Small differences, probably not large enough to account for the differences in mutation frequencies, were seen. However, when synchronized S-phase-enriched cell populations were examined, substantial differences were seen, both in whole-cell extracts and in nuclear extracts. Thy- 303 cells, which have higher mutation frequencies than do Thy- 49 cells, also showed the more aberrant dNTP pools. These data indicate that the Thy- 303 line contains a second mutation in addition to the mutation affecting CTP synthetase control. Evidence suggests that this putative second mutation affects an allosteric regulatory site of ribonucleotide reductase. The data on intranuclear dNTP pools in synchronized S-phase cells indicate that higher proportions of cellular dATP and dGTP are found in the nucleus than are corresponding amounts of dCTP and dGTP. Thus, despite the porous nature of the nuclear membrane, there are conditions under which the distributions of deoxyribonucleotides across this membrane are not random.
Mol Cell Biol 1991 Jan
PMID:Cell cycle-dependent variations in deoxyribonucleotide metabolism among Chinese hamster cell lines bearing the Thy- mutator phenotype. 198 19

The sequence of the DIN1 gene of Saccharomyces cerevisiae is identical to RNR3, a gene encoding a DNA damage-inducible regulatory subunit of ribonucleotide reductase. Two sequence elements located upstream of DIN1 (RNR3) are homologous to putative DNA damage regulatory elements in the promoter of the reductase catalytic subunit gene, RNR2. The transcript start sites for DIN1(RNR3) have been localized, and induction by different agents has been compared with other DNA damage-regulated genes.
Mol Cell Biol 1990 Oct
PMID:The DNA damage-inducible gene DIN1 of Saccharomyces cerevisiae encodes a regulatory subunit of ribonucleotide reductase and is identical to RNR3. 220 19

The new deoxycytidine analogue 2',2'-difluorodeoxycytidine (dFdC) is a specific inhibitor of DNA synthesis that has marked cytotoxicity and therapeutic activity. A 2-hr incubation with 0.1-10 microM dFdC decreased cellular viability 78-97%. This treatment reduced deoxynucleoside triphosphate pools, similar to the action of the ribonucleotide reductase inhibitor hydroxyurea. The most pronounced decrease occurred in the dCTP pool, quantitatively followed by the decrease of dATP, dGTP, and dTTP. In contrast, inhibition of DNA synthesis by arabinosylcytosine did not affect the dCTP level, whereas dATP, dGTP, and dTTP pools increased, but less than 2-fold. The incorporation of [5-3H]cytidine into the dCTP pool, a measure of ribonucleotide reductase activity in whole cells, was reduced to 3% of controls by 0.1 microM dFdC, but to only 40% by 0.1 microM ara-C. Each drug decreased incorporation of [5-3H]cytidine into DNA to a similar extent (greater than 94%), suggesting limitation by a reaction proximal to this step. The cellular concentration of dFdC 5'-diphosphate was 0.3 microM at 50% inhibition of the in situ activity of ribonucleotide reductase. Direct assays of partially purified ribonucleoside diphosphate reductase (EC 1.17.4.1) demonstrated 50% inhibition by 4 microM dFdC 5'-diphosphate; dFdC 5'-triphosphate was much less inhibitory. We conclude that dFdC 5'-diphosphate acts as an inhibitor of ribonucleoside diphosphate reductase.
Mol Pharmacol 1990 Oct
PMID:Inhibition of ribonucleotide reduction in CCRF-CEM cells by 2',2'-difluorodeoxycytidine. 223 93

JB3-B is a Chinese hamster ovary cell mutant previously shown to be temperature sensitive for DNA replication (J. J. Dermody, B. E. Wojcik, H. Du, and H. L. Ozer, Mol. Cell. Biol. 6:4594-4601, 1986). It was chosen for detailed study because of its novel property of inhibiting both polyomavirus and adenovirus DNA synthesis in a temperature-dependent manner. Pulse-labeling studies demonstrated a defect in the rate of adenovirus DNA synthesis. Measurement of deoxyribonucleoside triphosphate (dNTP) pools as a function of time after shift of uninfected cultures from 33 to 39 degrees C revealed that all four dNTP pools declined at similar rates in extracts prepared either from whole cells or from rapidly isolated nuclei. Ribonucleoside triphosphate pools were unaffected by a temperature shift, ruling out the possibility that the mutation affects nucleoside diphosphokinase. However, ribonucleotide reductase activity, as measured in extracts, declined after cell cultures underwent a temperature shift, in parallel with the decline in dNTP pool sizes. Moreover, the activity of cell extracts was thermolabile in vitro, consistent with the model that the JB3-B mutation affects the structural gene for one of the ribonucleotide reductase subunits. The kinetics of dNTP pool size changes after temperature shift are quite distinct from those reported after inhibition of ribonucleotide reductase with hydroxyurea. An indirect effect on ribonucleotide reductase activity in JB3-B has not been excluded since human sequences other than those encoding the enzyme subunits can correct the temperature-sensitive growth defect in the mutant.
Mol Cell Biol 1990 Nov
PMID:Temperature-sensitive DNA mutant of Chinese hamster ovary cells with a thermolabile ribonucleotide reductase activity. 223 12


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