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 RNAtemplate 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.