RELEASE OF 5'-TERMINAL DEOXYRIBOSE-PHOSPHATE RESIDUES FROM INCISED ABASIC SITES IN DNA BY THE ESCHERICHIA-COLI RECJ PROTEIN

Excision of deoxyribose-phosphate residues from enzymatically incised abasic sites in double-stranded DNA is required prior to gap-filling a nd ligation during DNA base excision-repair, and a candidate deoxyribo phosphodiesterase (dRpase) activity has been identified in E.coli. Thi s activity is shown here to be a function of the E.coli RecJ protein, previously described as a 5'-->3' single-strand specific DNA exonuclea se involved in a recombination pathway and in mismatch repair. Highly purified preparations of dRpase contained 5'-->3' exonuclease activity for single-stranded DNA, and homogeneous RecJ protein purified from a n overproducer strain had both 5'-->3' exonuclease and dRpase activity . Moreover, E.coli recJ strains were deficient in dRpase activity. The hydrolytic dRpase function of the RecJ protein requires Mg2+; in cont rast, the activity of E.coli Fpg protein, that promotes the liberation of 5'-->3' Rp residues from DNA by beta-elimination, is suppressed by Mg2+. Several other E.coli nucleases, including exonucleases I, III, V, and VII, endonucleases I, III and IV and the 5'-->3' exonuclease fu nction of DNA polymerase I, are unable to act as a dRpase. Nevertheles s, E.coli fpg recJ double mutants retain capacity to repair abasic sit es in DNA, indicating the presence of a back-up excision function.