Favored incorporation of a correct dNTP over an incorrect dNTP. 
When an incorrect dNTP enters the insertion site on Pol I, binding is readily reversed (back arrow). 
In the rare instance of incorporation of the incorrect dNTP, the process is slow due to the imperfect active- 
In the favored (rapid) route, the mispaired 3′ terminus is shifted to the 3′→5′ exonuclease, and in 
the mismatched nucleotide is excised to re- 
This allows Pol I to insert the correct nucleotide on the second try. Binding and incorporation of a correct dNTP is rapid and paves the way for the next round of incorporation. 
If the incorrect nucleotide remains, the mismatched DNA is slow to act as substrate for the next round of dNTP incorporation.
When an incorrect dNTP enters the insertion site on Pol I, binding is readily reversed (back arrow). In the rare instance of incorporation of the incorrect dNTP, the process is slow due to the imperfect activ In the favored (rapid) route, the mispaired 3′ terminus is shifted to the 3′→5′ exonuclease, and in the mismatched nucleotide is excised to r This allows Pol I to insert the correct nucleotide on the second try. Binding and incorporation of a correct dNTP is rapid and paves the way for the next round of incorporation. If the incorrect nucleotide remains, the mismatched DNA is slow to act as substrate for the next round of dNTP incorporation.