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 useful for example in
removing RNA primers.