polymerase1

DNA polymerase I is a bacterial DNA polymerase that was first purified from Escherichia coli in the late 1960s. The enzyme catalyzes the addition of deoxyribonucleotides to a DNA strand, playing a central role during DNA replication and repair. Unlike the highly processive polymerases found in eukaryotes, polymerase I operates with moderate processivity and functions primarily in Okazaki fragment maturation, removing RNA primers through its 5'→3' exonuclease activity before filling in the resulting gap with new DNA.

The enzyme consists of a large catalytic subunit and several accessory domains. Its N‑terminal domain carries 5'→3' exonuclease activity, while the central domain contains the polymerase active site. A C‑terminal 3'→5' exonuclease domain provides proofreading capability, enhancing fidelity. Structural studies have revealed that polymerase I adopts a conservative “right‑hand” motif common to many replicative polymerases, but its unique domain architecture allows coordination of nick‑translation and primer removal in a single enzyme.

Polymerase I has been a cornerstone of molecular biology methodologies. The proofreading activity of the Klenow fragment, a truncated form lacking the 5'→3' exonuclease domain, is routinely used for blunt‑end DNA synthesis and for creating single‑stranded DNA during sequencing reactions. More recently, polymerase I mutants with altered processivity or fidelity have been developed for specialized sequencing and DNA repair assays.

In summary, DNA polymerase I is a multifaceted bacterial enzyme critical for DNA replication fidelity and repair. Its distinct domain organization and dual enzymatic activities have made it a valuable tool in genetic research and biotechnology, while ongoing structural and functional studies continue to illuminate its mechanistic diversity.