Biological Diversity of DNA Polymerases

Many different polymerases have been discovered and, based on the primary sequence homologies (Braithwaite and Ito, 1993 Delarue et ah, 1990 Ito and Braithwaite, 1991) and crystal structure analyses (Joyce and Steitz, 1994), the different polymerases have been classified into seven different families A, B, C, D, X, Y, and RT. 

Eukaryotic replicative DNA polymerase a, 8, e, archaebacterial DNA polymerases, viral DNA polymerases, DNA polymerases encoded by mitochondrial plasmids of various fungi and plants, and some bacteriophage 

Bacterial family C polymerases are the major chromosomal replicative enzyme (Kornberg and Baker, 1992). Like other replicative polymerases, the holoenzyme interacts with other proteins and forms a large multisubunit complex consisting of at least 10 subunits (Kornberg and Baker, 1992). The a-subunit contains the DNA polymerase activity that is tightly associated with the e-subunit, which contains a 3 -5 exonuclease activity (Kelman and O Donnell, 1995). 

Known members of the family X polymerases include eukaryotic DNA polymerase [1 (pol fi) (Abbotts et al., 1988), polymerase a (Burgers et al, 2001), polymerase fi (Dominguez et al, 2000), polymerase X (Garcia-Diaz et al, 2000), yeast polymerase IV (Prasad et al, 1993), and the African swine fever virus polymerase X (Martins et al, 1994). Pol [1 is known to be involved in the base excision repair (BER) pathway, which is important for repairing 

UmuC polymerases, which are also known as DNA polymerase IV and V in E. coli, respectively, and from eukaryotes, the Revl (pol 0 and Rad30 (pol rj) polymerases (Yang, 2003 Zhou et al, 2001). 

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