DETECTION AND CHARACTERIZATION OF DNA-POLYMERASE-ACTIVITY IN TOXOPLASMA-GONDII

A DNA polymerase activity has been detected and characterized in crude extracts from tachyzoites of Toxoplasma gondii. The enzyme has a sedi mentation coefficient of 6.4 S, corresponding to an approximate molecu lar weight of 150000 assuming a globular shape. Like mammalian DNA pol ymerase alpha, the DNA polymerase of T. gondii was sensitive to N-ethy lmaleimide and inhibited by high ionic strength. However, the enzyme a ctivity was not inhibited by aphidicolin which is an inhibitor of mamm alian DNA polymerases alpha, delta and epsilon and also cytosine-beta- D-arabinofuranoside-5'-triphosphate which is an inhibitor of alpha pol ymerase. The activity was inhibited by 2',3'-dideoxythymidine-5'-triph osphate which is an inhibitor of mammalian DNA polymerase beta and gam ma. Magnesium ions (Mg2+) were absolutely required for activity and it s optimal concentration was 6 mm. The optimum potassium (K+) concentra tion was 50 mm and a higher concentration of K+ markedly inhibited the activity. Activity was optimal at pH 8. Monoclonal antibodies against human DNA polymerase alpha did not bind to DNA polymerase of T. gondi i. Thus the T. gondii enzyme differs from the human enzymes and may be a useful target for the design of toxoplasmacidal drugs.