COMPARISON AMONG DNA-POLYMERASE-1, DNA-POLYMERASE-2 AND DNA-POLYMERASE-3 FROM MAIZE EMBRYO AXES - A DNA PRIMASE ACTIVITY COPURIFIES WITH DNA-POLYMERASE 2

Three DNA polymerase activities, named 1, 2 and 3 were purified from m aize embryo axes and were compared in terms of ion requirements, optim al pH, temperature and KCl for activity, response to specific inhibito rs and use of templates. All three enzymes require a divalent cation f or activity, but main differences were observed in sensitivity to inhi bitors and template usage: while DNA polymerases 1 and 2 were inhibite d by N-ethyl maleimide and aphidicolin, inhibitors of replicative-type enzymes, DNA polymerase 3 was only marginally or not affected at all. In contrast, DNA polymerase 3 was highly inhibited by very low concen trations of ddTTP, an inhibitor of repair-type enzymes, and a 100-fold higher concentration of the drug was needed to inhibit DNA polymerase s I and 2. Additionally, DNA polymerases 1 and 2 used equally or more efficiently the synthetic template polydA-oligodT: as compared to acti vated DNA, while polymerase 3 used it Very poorly. Whereas DNA polymer ases 1 and 2 shared properties of replicative-type enzymes, DNA polyme rase 3 could be a repair-type enzyme. Moreover, a DNA primase activity copurified with the 8000-fold purified DNA polymerase 2, strenghtenin g the suggestion that polymerase 2 is a replicative enzyme, of the alp ha-type. This DNA primase activity was also partially characterized. T he results are discussed in terms of relevant data about other plant D NA polymerases and primases reported in the literature.