An unusual mechanism for the major human apurinic/apyrimidinic (AP) endonuclease involving 5' cleavage of DNA containing a benzene-derived exocyclic adduct in the absence of an AP site.
The major human apurinic/apyrimidinic (AP) endonuclease (class II) is known to cleave DNA 5' adjacent to an AP site, which is probably the most common DNA damage produced hydrolytically or by glycosylase-mediated removal of modified bases. p-Benzoquinone (pBQ), one of the major benzene metabolites, reacts with DNA to form bulky exocyclic adducts. Herein we report that the human AP endonuclease directly catalyzes incision in a defined oligonucleotide containing 3,N4-benzetheno-2'-deoxycytidine (pBQ-dC) without prior generation of an AP site. The enzyme incises the oligonucleotide 5' to the adduct and generates 3'-hydroxyl and 5'-phosphoryl termini but leaves the pBQ-dC on the 5' terminus of the cleavage fragment. The AP function of the enzyme is not involved in this action, as no preexisting AP site is present nor is a DNA glycosylase activity involved. Nicking of the pBQ-dC adduct also leads to the same "dangling base" cleavage when two Escherichia coli enzymes, exonuclease III and endonuclease IV, are used. Our finding of this unusual mode of action used by both human and bacterial AP endonucleases raises important questions regarding the requirements for substrate recognition and catalytic active site(s) for this essential cellular repair enzyme. We believe this to be the first instance of the presence of a bulky carcinogen adduct leading to this unusual mode of action.
Hang
B
B
Life Sciences Division, Donner Laboratory, Lawrence Berkeley National Laboratory, University of California, Berkeley 94720, USA.
Chenna
A
A
Fraenkel-Conrat
H
H
Singer
B
B
D000595:Amino Acid Sequence; D001483:Base Sequence; D016227:Benzoquinones; D001665:Binding Sites; D018736:DNA Adducts / Q000737:chemistry / Q000378:metabolism*; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D003843:Deoxycytidine Monophosphate / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D043223:Deoxyribonuclease IV (Phage T4-Induced); D029968:Escherichia coli Proteins; D018922:HL-60 Cells; D006367:HeLa Cells; D006801:Humans; D008190:Lyases / Q000378:metabolism*; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000737:chemistry / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D014357:Trypsin
D016227:Benzoquinones; D018736:DNA Adducts; D029968:Escherichia coli Proteins; D009838:Oligodeoxyribonucleotides; D010446:Peptide Fragments; D003843:Deoxycytidine Monophosphate; C065824:(3'-hydroxy)-3,N(4)-benzetheno-1'-deoxycytidine 3'-phosphate; C004532:quinone; D043223:Deoxyribonuclease IV (Phage T4-Induced); C468972:endonuclease IV, E coli; D014357:Trypsin; D008190:Lyases; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase