Studies on the Processivity of Maize DNA Polymerase 2, an [alpha]-Type Enzyme

This paper describes studies on the processivity of an [alpha]-type DNA polymerase from maize (Zea mays L.) embryonic axes, designated as DNA polymerase 2. Using poly(dA)/oligo(dT) as template, DNA polymerase 2 has a processivity of 18 ([plus or minus]5) nucleotides incorporated, a value much lower than that found for wheat [alpha]-type DNA polymerase (P. Laquel, S. Litvak, M. Castroviejo [1993] Plant Physiol 102: 107-114). Conditions that maximally stimulate enzyme activity, such as 100 mM KCl and 12 mM Mg2+, are strongly inhibitory of processivity and cause the enzyme to become distributive under these conditions. Optimal concentrations for processivity are 10 mM KCl and 1 to 2 mM Mg2+. Both enzyme activity and processivity were found to be similar at different Mn2+ concentrations. Both DNA polymerase 2 activity and processivity are greatly reduced by spermine and N-ethylmaleimide. A distinguishing feature of processivity in DNA polymerase 2 was the response to ATP, which not only stimulated processivity by more than 2-fold, but also produced a distinctive pattern in which the enzyme seemed to pause every 10 nucleotides, reaching a value of 40 to 50 nucleotides incorporated. This pattern was observed in some, but not all, heparin-Sepharose fractions with enzyme activity, suggesting the possibility of different DNA polymerase 2 complexes.