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Gene Review

sbcB  -  exodeoxyribonuclease I; exonuclease I

Escherichia coli str. K-12 substr. MG1655

Synonyms: ECK2005, JW1993, cpeA, xonA
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Disease relevance of sbcB

  • The sbcB coding sequence contains many non-optimal codons, characteristic of many poorly expressed E. coli genes [1].
  • Recombinant lambda phages that complement the recombination and repair defects of recN recBC sbcB mutants have been identified, and the recN gene has been cloned from these phages into a low copy-number plasmid [2].
  • At the right terminus, the relevant junction sequences from MRV and myxoma could not be cloned in wild-type Escherichia coli but were maintained stably in a recA recBC sbcB host [3].

High impact information on sbcB

  • We propose that DNA replication drives the extrusion of palindromic sequences in vivo, forming secondary structures that are substrates for the recBC and sbcB gene products [4].
  • Determination of the nucleotide sequence for the exonuclease I structural gene (sbcB) of Escherichia coli K12 [1].
  • The results strongly suggest that 3' (rho) 5' single-stranded DNA ends constitute an important component in recombination pathway involved in DNA double-strand break repair and that absence of sbcB from deinococcal genome may significantly aid its extreme radioresistance phenotype [5].
  • The gene is located at min 44 of the E. coli genetic map, close to the sbcB gene. sbmC expression is induced by DNA-damaging agents and, also, by the entry of cells into the stationary growth phase [6].
  • A strain containing a deletion of the sbcB gene showed little dRpase activity; the activity could be restored by transformation of the strain with a plasmid containing the sbcB gene [7].

Chemical compound and disease context of sbcB


Biological context of sbcB

  • The rate of recombination of circular dimer plasmids was at least 1000-fold higher in recB recC sbcB or recB recC sbcA mutants as compared to wild-type cells [9].
  • Physical analysis of linear dimer- or circular dimer-transformed recB recC sbcB mutants revealed that all transformants contained recombinant monomer genotypes [9].
  • In addition, mutation in either sbcA or sbcB supresses the Vrm- phenotype of dam-3 recB21 recC22 strains [10].
  • When relocated to the recQ site on the chromosome, the recQ::Tn3 mutations conferred partial resistance to thymineless death (TLD) or, in the case of a recBC sbcB background, recombination deficiency and increased UV sensitivity [11].
  • They also act with sbcB mutations as cosuppressors of the defects in recombination, DNA repair, and cell viability associated with recBC mutations [12].

Regulatory relationships of sbcB

  • The mechanism by which an sbcB mutation suppresses the deficiency in postreplication repair shown by recB recC mutants of Escherichia coli was studied [13].

Other interactions of sbcB

  • Indirect but not direct stimulation was also dependent on recJ (coding for a 5'-to-3' exonuclease specific for single-stranded DNA) regardless of sbcA or sbcB configuration [14].
  • The results also show that the recF144 mutation in recBC sbcB recF and recF cells leads to the absence of detectable amounts of a 49,000 molecular weight protein [15].
  • This requirement is suppressed by either an additional sbcA or sbcC mutation, but not by an sbcB mutation [16].
  • Cultures of recBC sbcB (sbcC+) strains grow slowly, contain many inviable cells, and rapidly accumulate fast-growing variants due to mutation of sbcC. sbcC has been identified on recombinant plasmids and tentatively located by Tn1000 mutagenesis to a 0.9-kilobase DNA section between proC and phoR [17].
  • Mutation of the recN gene of Escherichia coli in a recBC sbcB genetic background blocks conjugational recombination and confers increased sensitivity to UV light and mitomycin C [2].


  1. Determination of the nucleotide sequence for the exonuclease I structural gene (sbcB) of Escherichia coli K12. Phillips, G.J., Kushner, S.R. J. Biol. Chem. (1987) [Pubmed]
  2. Repair of DNA double-strand breaks in Escherichia coli K12 requires a functional recN product. Picksley, S.M., Attfield, P.V., Lloyd, R.G. Mol. Gen. Genet. (1984) [Pubmed]
  3. Tumorigenic poxviruses: fine analysis of the recombination junctions in malignant rabbit fibroma virus, a recombinant between Shope fibroma virus and myxoma virus. Upton, C., Macen, J.L., Maranchuk, R.A., DeLange, A.M., McFadden, G. Virology (1988) [Pubmed]
  4. Large palindromes in the lambda phage genome are preserved in a rec+ host by inhibiting lambda DNA replication. Shurvinton, C.E., Stahl, M.M., Stahl, F.W. Proc. Natl. Acad. Sci. U.S.A. (1987) [Pubmed]
  5. An exonuclease I-sensitive DNA repair pathway in Deinococcus radiodurans: a major determinant of radiation resistance. Misra, H.S., Khairnar, N.P., Kota, S., Shrivastava, S., Joshi, V.P., Apte, S.K. Mol. Microbiol. (2006) [Pubmed]
  6. sbmC, a stationary-phase induced SOS Escherichia coli gene, whose product protects cells from the DNA replication inhibitor microcin B17. Baquero, M.R., Bouzon, M., Varea, J., Moreno, F. Mol. Microbiol. (1995) [Pubmed]
  7. DNA deoxyribophosphodiesterase of Escherichia coli is associated with exonuclease I. Sandigursky, M., Franklin, W.A. Nucleic Acids Res. (1992) [Pubmed]
  8. Efficient introduction of cloned mutant alleles into the Escherichia coli chromosome. Kulakauskas, S., Wikström, P.M., Berg, D.E. J. Bacteriol. (1991) [Pubmed]
  9. Genetic and physical analysis of plasmid recombination in recB recC sbcB and recB recC sbcA Escherichia coli K-12 mutants. Luisi-DeLuca, C., Lovett, S.T., Kolodner, R.D. Genetics (1989) [Pubmed]
  10. Isolation and characterization of Dam+ revertants and suppressor mutations that modify secondary phenotypes of dam-3 strains of Escherichia coli K-12. McGraw, B.R., Marinus, M.G. Mol. Gen. Genet. (1980) [Pubmed]
  11. The recQ gene of Escherichia coli K12: molecular cloning and isolation of insertion mutants. Nakayama, K., Irino, N., Nakayama, H. Mol. Gen. Genet. (1985) [Pubmed]
  12. Identification of sbcD mutations as cosuppressors of recBC that allow propagation of DNA palindromes in Escherichia coli K-12. Gibson, F.P., Leach, D.R., Lloyd, R.G. J. Bacteriol. (1992) [Pubmed]
  13. Mechanism of sbcB-suppression of the recBC-deficiency in postreplication repair in UV-irradiated Escherichia coli K-12. Wang, T.C., Smith, K.C. Mol. Gen. Genet. (1985) [Pubmed]
  14. Indirect stimulation of recombination in Escherichia coli K-12: dependence on recJ, uvrA, and uvrD. Schellhorn, H.E., Low, K.B. J. Bacteriol. (1991) [Pubmed]
  15. The recF-dependent endonuclease from Escherichia coli K12. Formation and resolution of pBR322 DNA multimers. Krivonogov, S.V. Mol. Gen. Genet. (1984) [Pubmed]
  16. Expression of the recA gene in recombination-deficient (rec-) strains of Escherichia coli. Chua, K.L., Mak, Y.K., Oliver, P. Biochimie (1993) [Pubmed]
  17. Identification and genetic analysis of sbcC mutations in commonly used recBC sbcB strains of Escherichia coli K-12. Lloyd, R.G., Buckman, C. J. Bacteriol. (1985) [Pubmed]
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