The Klenow fragment is a large protein fragment produced when DNA polymerase I from E. coli is enzymatically cleaved by the protease subtilisin. First reported in 1970, it retains the 5'-3' polymerase activity and the 3’ → 5’ exonuclease activity for removal of precoding nucleotides and proofreading, but loses its 5' → 3' exonuclease activity.
The other smaller fragment formed when DNA polymerase I from E. coli is cleaved by subtilisin retains the 5'-3' exonuclease activity but does not have the other two activities exhibited by the Klenow fragment (i.e. 5'-> 3' polymerase activity, and 3'->5' exonuclease activity).
Read more about Klenow Fragment: Research, The Exo- Klenow Fragment
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