The isolation and characterization of DNA polymerase alpha from spinach

A DNA polymerase with the characteristics of the alpha class of eukaryotic DNA polymerases has been purified 1000-fold from spinach leaves. The enzyme has a molecular weight of 160,000 +/- 10,000 in its native form and is markedly inhibited by aphidicolin and N-ethylmaleimide, but not by dideoxynucleoside triphosphates. As isolated, the enzyme contains no detectable deoxyribonuclease activity. A catalytically active 12-kilodalton fragment of the DNA polymerase, apparently generated by endogenous proteolytic action, has also been purified. The native enzyme is found predominantly in the cytoplasmic fraction of broken leaf cell preparations and less than 10% is found associated with the nuclei.