E. coli Polymerase I is a product of polA gene that consists of 5′-3′ polymerase activity and both 3′-5′ and 5′-3′ exonuclease activity. In vivo, Pol I takes part in DNA synthesis and DNA repair. The 5′-3′ exonuclease activity of Pol I makes it unsuitable for many applications in vitro. However, it is found that a protease known as subtilisin, can cleave Pol I into a small fragment, which contains the 5′ -> 3′ exonuclease activity, and a large fragment that consists of both 5′-3′ polymerase activity and 3′-5′ exonuclease activity called Klenow Continue Reading →