Single-stranded-DNA-specific exonuclease acting in a 5' to 3' direction; has no detectable activity on ssRNA. Requires a divalent cation; Mg(2+) > Mn(2+) > Co(2+). Structures with 1 Mg(2+), or 1 or 2 Mn(2+) were determined; the authors conclude 2 metal ions are required for activity. kcat for ssDNA remains unchanged as chain length increases from 6-mers to 21-mers. Monomer. Intact protein binds ss- but not dsDNA. Belongs to the RecJ family.