a 5'-end 5'-dephospho-2'-deoxyribonucleotidyl-2'-deoxyribonucleotide in single-stranded DNA + H2O = a 5'-end dephospho-2'-deoxyribonucleoside in single-stranded DNA + a 2'-deoxyribonucleoside 3'-phosphate + H(+) — reaction