Pol II

DNA Polymerase II
Crystal Structure of DNA pol II (Based on PDB entry 3K5M)
Identifiers
Organism	Escherichia coli (str. K-12 substr. MG1655)
Symbol	polB
Entrez	944779
PDB	3K5M
RefSeq (Prot)	NP_414602.1
UniProt	P21189
Other data
EC number	2.7.7.7
Chromosome	genome: 0.06 - 0.07 Mb

DNA polymerase II (also known as DNA Pol II or Pol II) is a prokaryotic DNA-Dependent DNA polymerase encoded by the PolB gene.

DNA Polymerase II is an 89.9-kDa protein and is a member of the B family of DNA polymerases. It was originally isolated by Thomas Kornberg in 1970, and characterized over the next few years.

The in vivo functionality of Pol II is under debate, yet consensus shows that Pol II is primarily involved as a backup enzyme in prokaryotic DNA replication. The enzyme has 5’ → 3’ DNA synthesis capability as well as 3’ → 5’ exonuclease proofreading activity. DNA Pol II interacts with multiple binding partners common with DNA Pol III in order to enhance its fidelity and processivity.

DNA Polymerase I was the first DNA-Directed DNA polymerase to be isolated from E. coli. Several studies involving this isolated enzyme indicated that DNA pol I was most likely involved in repair replication and was not the main replicative polymerase. In order to better understand the in vivo role of DNA pol I, E. coli mutants deficient in this enzyme (termed Pol A1⁻) were generated in 1969 by De Lucia and Cairns. As characterized, this new mutant strain was more sensitive to ultraviolet light, corroborating the hypothesis that DNA pol II was involved in repair replication. The mutant grew at the same rate as the wild type, indicating the presence of another enzyme responsible for DNA replication. The isolation and characterization of this new polymerase involved in semiconservative DNA replication followed, in parallel studies conducted by several labs. The new polymerase was termed DNA polymerase II, and was believed to be the main replicative enzyme of E. coli for a time. DNA pol II was first crystallized by Anderson et. Al in 1994.