T4 DNA Polymerase catalyzes the synthesis of DNA in the 5´→ 3´ direction and requires the presence of template and primer. This enzyme has a 3´→ 5´ exonuclease activity which is much more active than that found in DNA Polymerase I (E. coli).  Unlike E. coli DNA Polymerase I, T4 DNA Polymerase does not have a 5´→ 3´ exonuclease function.