Putative 5'->3' double-stranded DNA exonuclease which may also contain a cryptic 3'->5' double-stranded DNA exonuclease activity. May be involved in DNA mismatch repair (MMR) (By similarity). Binds 2 magnesium ions per subunit. They probably participate in the reaction catalyzed by the enzyme. May bind an additional third magnesium ion after substrate binding. Belongs to the XPG/RAD2 endonuclease family. EXO1 subfamily.