The Structure of DNA Polymerase I Klenow Fragment Bound to Duplex DNA
Background:
KLENOW FRAGMENT of DNA POL I
by, Sundeep Kang
DNA Pol I consists of a single polypeptide, 928 redisues in lengh. Pol I was the first DNA polymerase discovered, and it was thought to be responsible for the DNA replication. Pol I links two deoxynucleoside triphosphates; the second dNTP must be linked to the free 3-OH of the previous nucleoside. The release and subsequent hydrolysis of PPi drives the process, and the specificity of the which nucleoside will be added to the growing polynucleoside chain results from the fact that the incoming dNTP must form Watson-Crick base pairs with the template strand of DNA from which the copy is made. The entire Pol I enzyme consists of polymerase activitity, in addition to 5`-3` and 3`-5` exonuclease activity. All three occupy different active sites on the enzyme, however when proteases are added the enzyme breaks down into two fragments. The larger fragment known as the Klenow Fragment is about 604 residues contains the polymerase active site as well as the 3`-5` exonuclease active site. This Klenows was crystallized in "editing mode", where the protein exhibits exonuclease activity. When the protein is "polymerizing mode" the polymerae site is active.