T4 DNA Polymerase from bacteriophage T4 is the mezophilic polymerase, exhibiting very strong 3’→5′ exonuclease activity. The polymerase requires the presence of a single-stranded DNA template and a primer. Exonuclease, stronger than that found in DNA Polymerase I, is more active on single-stranded DNA than on double-stranded DNA. Exonuclease activity can be used to remove one or a few nucleotides from 3′-end of double–stranded DNA. Enzyme suitable for: 3′ overhang removal to form blunt ends, 5′ fill-in to form blunt ends, probe labeling using replacement synthesis, single strand deletion subcloning, second strand synthesis in site-directed mutagenesis.