Klenow fragment lacks the activity of?
(A) 3'-5' exonuclease (B) 5'-3' exonuclease (C) 5'-3' DNA polymerase (D) 3'-5' DNA polymerase
(B) Ans: B. 5'-3' exonucleaseDNA polymerase I is not the primary enzyme of replication; instead, it performs a host of clean-up functions during replication, recombination, and repair.When the 5'-3' exonuclease domain is removed, the remaining fragment (Mr 68,000), the large fragment or Klenow fragment, retains the polymerization and proofreading activities.Klenow fragment is a large protein fragment produced when DNA polymerase I from E. coli is enzymatically cleaved by the protease subtilisin.