ABSTRACT
DNA polymerases DNA polymerase I from E. coli catalyzes the stepwise addition of deoxyribonucleotides to the 3¢-OH end of a DNA chain:
dNTP Æ (DNA) n+1 PP
The enzyme has the following requirements:
z All four dNTPs (dATP, dGTP, dTTP and dCTP) must be present to be used as precursors; Mg2+ is also required
DNA polymerase I is a template-directed enzyme, that is it recognizes the next nucleotide on the DNA template and then adds a complementary nucleotide to the 3¢-OH of the primer, creating a 3¢5¢ phosphodiester bond, and releasing pyrophosphate. The reaction is shown in Figure 1. It involves nucleophilic attack of the 3¢-OH of the primer on the a-phosphate group of the incoming nucleotide. The primer is extended in a 5¢ Æ 3¢ direction.
