Exonuclease activities of DNA Polymerases

    An exonuclese is an enzyme that removes nucleotides. Most DNA Polymerases, whose primary function is to add nucleotides in the 5'3' direction, also have exonuclease activities. (A) 3'-5' exonuclease activity performs a 'proof reading' function by removing a nucleotide that has just been added incorrectly. (B) 5'-3' exonuclease activity displaces nucleotides ahead of the addition by polymerase activity: this is used for example in removing RNA primers.
