The T4 DNA Polymerase is a DNA polymerase originally isolated from the T4 Bacteriophage. Like the E. coli DNA Polymerase I, it has a 5’-3’ polymerase activity active at 37 °C. It features a particularly stronger 3’-5’ exonuclease proofreading activity that is more active on single stranded DNA than on double stranded. In addition, the polymerase activity requires a primed single strand of DNA, duplex DNA with gaps, or single stranded DNA with a protruding 5’ end. This polymerase is recommended for blunting, site-specific mutagenesis, and DNA gap filling.