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Abstract
Exonuclease VIII is an enzyme whose synthesis is induced as a result of sbcA mutations. The enzyme has been purified to near homogeneity from an Escherichia coli strain containing an sbcA mutation and mutations in the structural genes for exonuclease III, exonuclease V, and endonuclease I. The enzyme specifically degrades linear duplex DNA in a reaction which requires magnesium ions and is susceptible to inhibition by other divalent cations and by sulfhydryl-blocking reagents. Enzyme activity occurs over a broad pH range with peak activity at pH 8.5 in Tris buffer. The protein has a subunit Mr = 140,000, a sedimentation coefficient of 8.4 +/- 0.6, and a Stokes radius of 142 +/- 6 A, which is consistent with its active form being a multimer. Exonuclease VIII has a frictional coefficient of 2.6 which indicates that it has an asymmetric structure.
Highlights
Exonuclease VI11 is an enzyme whose synthesis is recombination via the RecF pathway requires the producotfs induced as a result of sbcA mutations
The enzyme de- structural gene forexonuclease I, xonA, andithas been grades linear duplex DNA in a reaction which requires proposed that sbcB activates the RecF pathwbayyeliminating magnesium ions and is susceptible to inhibition by inhibition of the RecF pathway by exonuclease I [3, 12, 15]
SbcA leads to the induction of recE, the structural gene for exonuclease VI11 [3,5]
Summary
From the Departmentof Biological Chemistry, Harvard MedicalSchool and the Laboratory of Molecular Genetics, DanaFarber Cancer Institute, Boston, Massachusetts02115. Exonuclease VI11 is an enzyme whose synthesis is recombination via the RecF pathway requires the producotfs induced as a result of sbcA mutations. Thesuggestion that sbcA is a mutation in a repressor geneis supportedby the observation thastbcA+ is dominantto sbcA- in amerodiploid[13].More recent results suggest that sbcA mutations may beof several different classes, each of which produce a similar phenotype but via different mechanisms [17, 18].Conceivably, exonuclease VI11 serves as the meabnyswhich sbcA activates the RecF pathway Genetic analysis in Escherichia coli has led to the isolation of recombination. That themreay be somerelationship between which map at 31 and 44 min, respectively [11,12,13,14] It hasbeen rac and sbcA is further supportebdy the observation thasbt cA suggested that sbcA and sbcB activate the RecF recombinationmutations cannotbe isolated in rac- strains [14]. Conjugational one sbcA mutation appears tobe a deletion extendingin from
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