(Science: enzyme molecular biology) enzymes 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 and polymerases, with apparently responsible for replication of nuclear dna and 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.