Processiveness of DNA polymerases. A comparative study using a simple procedure.

In this communication, we describe a simple procedure for analyzing the processiveness of DNA polymerases in general. By choosing conditions for which the number of incorporations per available primer is less than 1, we have reduced the probability of a primer molecule being utilized by the enzyme more than once. The primer-template used was poly(dA)300:oligo(dT)10, and the product was isolated by oligo(dT)-cellulose chromatography. The number of dTMP residues added per association was determined from the [3H]dThd + [3'-3H]dTMP/[3H]dThd ratio of the product after its digestion by micrococcal nuclease and spleen phosphodiesterase. Using this procedure, we have found that Escherichia coli DNA polymerase I, T4 DNA polymerase, and calf thymus alpha- and beta-DNA polymerase are "quasi-processive." Most of these enzymes add on the average approximately 10 to 15 nucleotides before dissociating from the template. T5 DNA polymerase, on the other hand, is processive, i.e. it continues to replicate a given template until it is very close to the 5' end of the template. With "nicked DNA-like" poly(dA):oligo(dT), the processiveness of E. coli DNA polymerase I is increased 2- to 2.5-fold. The significance of this increase in determining the "patch size" during DNA repair is discussed.