Klenow fragment

The Klenow fragment is a large protein fragment produced when DNA polymerase I from E. coli is enzymatically cleaved by the protease subtilisin.

Because the 5' → 3' exonuclease activity of DNA polymerase I from E. coli makes it unsuitable for many applications, the Klenow fragment, which lacks this activity, can be very useful in research.

The Klenow fragment is extremely useful for research-based tasks such as: The Klenow fragment was also the original enzyme used for greatly amplifying segments of DNA in the polymerase chain reaction (PCR) process,[2] before being replaced by thermostable DNA polymerases such as Taq polymerase.

This problem can be overcome by introducing mutations in the gene that encodes Klenow.

The exo-Klenow fragment is used in some fluorescent labeling reactions for microarray, and also in dA and dT tailing, an important step in the process of ligating DNA adapters to DNA fragments, frequently used in preparing DNA libraries for Next-Gen sequencing.