DNA polymerases

Enzymes (EC 2.7.7.7) involved in template-directed synthesis of DNA from deoxyribonucleotide triphosphates. I, II and III are known in E. coli ; III appears to be most important in genome replication and I is important for its ability to edit out unpaired bases at the end of growing strands. Animal cells have a, b and g polymerases, with a apparently responsible for replication of nuclear DNA, and g for replication of mitochondrial. All these function with a DNA strand as template. Retroviruses possess a unique DNA polymerase (reverse transcriptase) that uses an RNA template.