Recombinant Bacillus phage phi29 DNA polymerase (2), partial

Polymerase responsible for protein-primed viral DNA replication by strand displacement with high processivity and fidelity. To start replication, the DNA polymerase forms a heterodimer with a free primer terminal protein (TP), recognizes the replication origins at both 5' ends of the linear chromosome, and initiates replication using as primer the OH-group of Ser-232 of the TP. This polymerase possesses three enzymatic activities: DNA synthesis (polymerase), primer terminal protein (TP) deoxynucleotidylation, which is the formation of a covalent linkage (phosphoester) between the hydroxyl group of a specific serine residue in TP and 5'-dAMP, a reaction directed by the second T at the 3' end, and 3' to 5' exonuclease activity. Exonuclease activity has a proofreading purpose. DNA polymerase edits the polymerization errors using an intramolecular pathway as the primer terminus travels from one active site to the other without dissociation from the DNA. DNA polymerization catalyzed by the DNA polymerase is a highly accurate process, but the protein-primed initiation is a quite inaccurate reaction. Since the polymerase initiates the replication on the second thymine, the TP-dAMP initiation product translocates backwards to recover the template information of the first nucleotide (sliding back-mechanism).