Klenow Fragment,DNA Polymerase,Enzymatic Reactions ,Exonuclease Activity

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	Klenow Fragment - E. coli DNA polymerase I consists of a single polypeptide chain. Pol I carries out three enzymatic reactions that are performed by three distinct functional domains. Two fragments are obtained when DNA pol I is treated with trypsin/subtilisin in mild conditions. The larger fragment is called as klenow fragment. This fragment is 602 amino acids in length. The function of the klenow fragment is to add nucleotides to the 3 end and 3 -5 exonuclease activity.
Klenow fragment adds nucleotides by using complementary strand as reference. It cannot extend the DNA without the presence of the complementary strand. If any nucleotide is added by mistake and the base pair is wrong (Le., if A is paired to G instead of T) then by using 3 -5 exonuclease activity present in klenow fragment, this mispaired base pair is removed. In general the klenow fragment has 5 -3 polymerase and exonuclease activity.