Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.4.1 (phosphodiesterase)
 18,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In Escherichia coli K-12, sbcB/xonA is the structural gene for exonuclease I, an enzyme that hydrolyzes single-stranded DNA to mononucleotides in the 3'-to-5' direction. This enzyme has been implicated in the DNA repair and recombination pathways mediated by the recB and recC gene products (exonuclease V). We have cloned several sbcB/xonA mutant alleles in bacterial plasmids and have partially characterized the cloned genes and their protein products. Two of the mutations (xonA2 and xonA6) retain no detectable exonucleolytic activity on single-stranded DNA. The xonA6 allele was shown to harbor an insertion of an IS30-related genetic element near the 3' end of the gene. Two other mutations, sbcB15 and xonA8, exhibited significantly reduced levels of exonuclease I activity as compared to the cloned wild-type gene. A correlation was observed between levels of exonuclease I activity and the ability of the sbcB/xonA mutations to suppress UV sensitivity in recB and recC strains. Also, recombinant plasmids bearing either the sbcB15 or xonA6 allele exhibited a high degree of instability during growth of their bacterial hosts. The results suggest that the sbcB/xonA gene product is a bi- or multifunctional protein that interacts with single-stranded DNA and possibly with other proteins in the suppression of genetic recombination and DNA-repair deficiencies in recB and recC mutants.
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PMID:Physical and biochemical characterization of cloned sbcB and xonA mutations from Escherichia coli K-12. 283 21

Plasmids containing sequences 3' of the adult beta 1 globin gene of Xenopus laevis are unstable on propagation in a range of E. coli host strains. Up to 300 bp of Xenopus DNA are lost by rec A independent recombination between (AT)37 and (AT)17 sequences. Additionally, smaller deletions occurring in or around the (AT)37 sequence are observed. Deletion of these potential cruciform structures occurs in the absence of exonuclease I, exonuclease V and exonuclease VIII as the same pattern of deletion events is observed in recA recBC sbcB and recBC sbcA recE strains.
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PMID:RecBC, sbcB independent, (AT)n-mediated deletion of sequences flanking a Xenopus laevis beta globin gene on propagation in E. coli. 301 63

Inactivation of RecBCD nuclease (exonuclease V) and SbcB nuclease (exonuclease I) in Escherichia coli K-12 diverts most of plasmid replication activity from circular monomer production to the synthesis of linear multimers. Linear multimer synthesis has been demonstrated in plasmids of diverse origins and copy numbers, including E. coli minichromosomes. The effect of dnaA, dnaB, recF, and recJ mutations on the rate of linear multimer synthesis in sbcB cells after gam inactivation of RecBCD nuclease was investigated. Results are consistent with the hypothesis that homologous recombination, but not activities at the plasmid origin of replication, is involved in initiation of linear multimer synthesis.
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PMID:Synthesis of linear multimers of OriC and pBR322 derivatives in Escherichia coli K-12: role of recombination and replication functions. 329 13

Shutoff of respiration is one of a number of recA+ lexA+ dependent (SOS) responses caused by far ultraviolet (245 nm) radiation (UV) damage of DNA in Escherichia coli cells. Thus far no rec/lex response has been shown to require the recB recC gene product, the RecBC enzyme. We report in this paper that UV-induced respiration shutoff did not occur in either of these radiation-sensitive derivatives of K12 strain AB1157 nor in the recB recC double mutant. The sbcB gene product is exonuclease I and it has been reported that the triple mutant strain recB recC sbcB has near normal recombination efficiency and resistance to UV. The sbcB strain shut off its respiration after UV but the triple mutant did not show UV-induced respiration shutoff; the shutoff and death responses were uncoupled. We concluded that respiration shutoff requires RecBC enzyme activity. The RecBC enzyme has ATP-dependent double-strand exonuclease activity, helicase activity and several other activities. We tested a recBC+ (double dagger) mutant strain (recC 1010) that had normal recombination efficiency and resistance to UV but which possessed no ATP-dependent double-strand exonuclease activity. This strain did not shut off its respiration. The presence or absence of other RecBC enzyme activities in this mutant is not known. These results support the hypothesis that ATP-dependent double-strand exonuclease activity is necessary for UV-induced respiration shutoff.
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PMID:RecBC enzyme activity is required for far-UV induced respiration shutoff in Escherichia coli K12. 351 Mar 70

The enzyme exonuclease I from Escherichia coli hydrolyzes successive nucleotides from the 3'-termini of single-stranded deoxyribonucleotide homopolymers. When the reaction is stopped after partial hydrolysis, only intact starting material and small oligomers can be isolated. The distribution of oligomeric products varies with the base composition of the polymer but the largest oligomer that can be isolated from the reaction of exonuclease I with homopolymers of deoxyadenylate, deoxythymidylate, or deoxycytidylate is a decamer. These results suggest a model in which exonuclease I possesses at least two nucleotide binding sites. When both sites are filled, with 11-mers and longer polymers, the enzyme does not dissociate from the polymer during hydrolysis. When, with smaller oligomers, only a single site is filled, the reaction partitions at each oligomer between hydrolysis and dissociation. The kinetics of the reactions of exonuclease I with purified polydeoxyriboadenylates of defined size distributions have been investigated. The maximum rates of hydrolysis are nearly independent of polymer size while the apparent Michaelis constants are inversely proportional to the polymer size. A simple steady state model yields a kinetic equation that is consistent with our results. Competition experiments indicate that the rate at which exonuclease I associates with the 3'-terminus of a polydeoxyribonucleotide is independent of the polymer's chain length.
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PMID:Processivity and kinetics of the reaction of exonuclease I from Escherichia coli with polydeoxyribonucleotides. 351 6

Linear plasmid multimers were identified in extracts of recB21 recC22 strains containing derivatives of the ColE1-type plasmids pACYC184 and pBR322. A mutation in sbcB increases the proportion of plasmid DNA as linear multimers. A model to explain this is based on proposed roles of RecBC enzyme and SbcB enzyme (DNA exonuclease I) in preventing two types of rolling-circle DNA synthesis. Support for this hypothesis was obtained by derepressing synthesis of an inhibitor of RecBC enzyme and observing a difference in control of linear multimer synthesis and monomer circle replication. Reinitiation of rolling-circle DNA synthesis was proposed to occur by recA+-dependent and recA+-independent recombination events involving linear multimers. The presence of linear plasmid multimers in recB and recC mutants sheds new light on plasmid recombination frequencies in various mutant strains.
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PMID:Synthesis of linear plasmid multimers in Escherichia coli K-12. 352 48

The complete nucleotide sequence of the structural gene for Escherichia coli exonuclease I has been determined. The coding region corresponds to a 465-amino acid protein with molecular weight of 53,174. The partial amino acid sequence of purified exonuclease I agrees with that predicted by the DNA sequence. Two putative weak promoters have been localized by S1 nuclease analysis. The sbcB coding sequence contains many non-optimal codons, characteristic of many poorly expressed E. coli genes.
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PMID:Determination of the nucleotide sequence for the exonuclease I structural gene (sbcB) of Escherichia coli K12. 353 37

The effects of Escherichia coli exonuclease I, exonuclease III, and deoxyribonucleic acid (DNA) polymerase on the biological activity of mature DNA from temperate Bacillus bacteriophage phi105 were investigated. Intact DNA loses infectivity rapidly upon exposure to exonuclease III. Although there is an overall decrease in marker rescue from exonuclease III-digested DNA, digestion preferentially affects markers at the end of the genetic map. This is taken to indicate a nonpermuted gene sequence in mature DNA. Incubation of mature DNA in the presence of exonuclease I or DNA polymerase has no effect on its biological activity. The possible structure of the ends of mature phi105 DNA is discussed. The rate of digestion of mature phi105 DNA by exonuclease III is only about 1/20 the rate of lambda DNA. Results of digestion of various DNA substrates by exonuclease III indicate that the enzyme distinguishes between different DNA terminal structures.
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PMID:Structure and biological activity of deoxyribonucleic acid from Bacillus bacteriophage phi 105: effects of Escherichia coli exonucleases. 432 11

Kilham rat virus (KRV) was grown in a rat nephroma cell line and was purified by two isopycnic centrifugations in cesium chloride. The virus contains single-stranded deoxyribonucleic acid (DNA) with a molecular weight of approximately 1.6 x 10(6). The DNA was extracted from the virion by both phenol extraction and by 2% sodium dodecyl sulfate at 50 C. KRV DNA, extracted by both procedures, was observed in an electron microscope by using a cytochrome c or diethylaminoethyldextran monolayer. The DNA was also exposed to exonuclease I, an enzyme which hydrolyzes specifically linear, single-stranded DNA. Hydrolysis of 70 to 80% of the DNA was observed. Both the enzymatic and the electron microscope studies support the conclusion that extracted KRV DNA is a single-stranded, linear molecule. The length of the DNA was measured in the electron microscope and determined to be 1.505 +/- 0.206 mum.
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PMID:Linear, single-stranded deoxyribonucleic acid isolated from Kilham rat virus. 432 90

recB(-)and recC(-) strains of Escherichia coli K12 are recombination deficient and sensitive to ultraviolet light and the drug, mitomycin C. We have reported that sbcB mutations indirectly suppress all three phenotypes and result in the loss of exonuclease I. In this publication we report the occurrence of other mutations that lead to loss of exonuclease I and indirectly suppress mitomycin and UV sensitivity but not recombination deficiency. These mutations (called xonA) are cotransducible with his and closely linked with sbcB. Both sbcB and xonA mutant strains appear to have identical residual amounts of nuclease activity on single-stranded DNA. It is hypothesized that exonuclease I possesses a second activity other than its known ability to degrade single-stranded DNA from a 3'-OH terminus. Accordingly, sbcB mutations would alter the second activity while xonA mutations would not.
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PMID:Indirect suppression of recB and recC mutations by exonuclease I deficiency. 455 61


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