DNA Polymerase I (Pol I) catalyzes the incorporation of dNTPs into double-stranded DNA in a 5'→3' direction that is complementary to the DNA or RNA template strand. It possesses 3'→5' exonuclease (proofreading) activity as well as 5'→3' exonuclease activity, making the enzyme useful for DNA end blunting and DNA labeling by nick translation. DNA Polymerase I is supplied in a buffer of 50 mM potassium phosphate (pH 6.5), 1 mM DTT and 50% glycerol.