It has been shown that, in the absence of dATP in the poly(dT) · oligo(dA) template-primer complex, the rate of primer cleavage by the E. coli DNA polymerase I Klenow fragment equals 4% of polymerization rate, while in the presence of dATP it equals as much as 50–60%. NaF and NMP taken separately inhibit exonuclease cleavage of oligo(dA) both with and without dATP. The addition of NaF (5–10 mM) or NMP (5–20 mM) increases the absolute increment of polymerization rate 5–9-fold relative to the absolute decrement of the rate of nuclease hydrolysis of primer. This proves the assumption that not more than 10–20% of primer molecules, interacting with the exonuclease center of polymerase, are cleaved by the enzyme. Presumably, NaF and nucleotides disturb the coupling of the 3'-end of oligonucleotide primer to the exonuclease center of the enzyme. As the primers mostly form complexes with the polymerizing center, the reaction of polymerization is activated.
