The sbcC and sbcD genes of Escherichia coli encode a nuclease involved in palindrome inviability and genetic recombination.
BACKGROUND
Long DNA palindromes have the potential to adopt hairpin or cruciform secondary structures that inhibit DNA replication. In Escherichia coli, this palindrome-mediated inviability results from the activity of the sbcC and sbcD genes, and genetic observations have suggested that they may encode a nuclease. Mutations in these genes also restore the defect in genetic recombination associated with recBC sbcB mutants.


RESULTS
We have purified the E. coli SbcCD protein from an overexpressing strain and have shown that it has an ATP-dependent DNA double-strand exonuclease activity. Co-purification of nuclease with protein, antibody inhibition and the absence of activity in extracts lacking the sbcCD genes confirm that the activity is intrinsic to SbcCD. The purified protein also has an ATP-independent single-strand DNA endonuclease activity.


CONCLUSIONS
We have shown that sbcCD encodes a nuclease. The purified protein has double-strand DNA exonuclease and single-strand DNA endonuclease activities. We propose that SbcCD cleaves secondary structures formed at replication forks and that the broken forks can be repaired by homologous recombination.
Connelly
J C
JC
Institute of Cell and Molecular Biology, University of Edinburgh, UK.
Leach
D R
DR
D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000378:metabolism; D003851:Deoxyribonucleases / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins; D005092:Exonucleases / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification; D005798:Genes, Bacterial / Q000502:physiology*; D008970:Molecular Weight; D009690:Nucleic Acid Conformation; D011995:Recombination, Genetic
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D029968:Escherichia coli Proteins; C061563:SbcC protein, Bacteria; C489229:SbcC protein, E coli; D000255:Adenosine Triphosphate; D003851:Deoxyribonucleases; D005092:Exonucleases; C081229:sbcD protein, E coli