(1) DNA polymerase domains DNA-directed DNA polymerase family B exonuclease (IPR006133), using a complementary DNA strand as a template, adds nucleotide triphosphate (dNTP) residues to the 5' end of a developing DNA strand. In all sequences in the B family, there is a DTDS motif. These sequences have different functional domains, such as a 5'-3' extension domain, a 3'-5' exonuclease domain, a DNA binding domain, and dNTP and pyrophosphate binding domains.