We show that purified, recombinant MRE11/RAD50 can cleave DNA at AP sites and that this AP-lyase activity is conserved from humans to Archaea.     ///    MRE11/RAD50 cleaves DNA in the AID/UNG-dependent pathway of immunoglobulin gene diversification..     ///    "MRE11/RAD50 cleaves at AP sites within single-stranded regions of DNA, suggesting that at transcribed Ig genes, cleavage may be coordinated with deamination by AID and deglycosylation by UNG2 to produce single-strand breaks (SSBs) that undergo subsequent mutagenic repair and recombination. "