Using a single isolation procedure and selective assays for the determination of enzyme activity, highly purified DNA-polymerases α, δ and ε were isolated from the lymphoma of Sprague-Dawley inbred rats. For pol α the subunit composition was 170, 70, 57 and 53 kDa with sedimentation coefficient 8.7 S for the native molecule; pol delta consists of two polypeptides (133 and 46 kDa; sedimentation coefficient 8.2 S), while pol ε is a single polypeptide (140 kDa) and its sedimentation coefficient is 7.0 S. Comparison of the interaction of individual enzymes with known inhibitors and proliferating cell nuclear antigen (PCNA) using the template-primer poly dA-oligo dT12-18, gave the following data: (i) pol α is selectively inhibited by N2-(p-butylphenyl)-2'-deoxyguanosine 5'-triphosphate (BuPdGTP) and stimulated by dimethyl sulfoxide; (ii) all the enzymes are inhibited by N-ethylmaleimide and aphidicolin; (iii) PCNA stimulates pol δ approximately 50 times while pol ε is moderately inhibited; (iv) pol α exhibits considerably higher DNA-primase activity with poly dC as template than with poly dT, and negligible 3'-5'-exonuclease activity whereas pol δ and pol ε, which do not exert any DNA-primase activity have approximately the same 3'-5'-exonuclease activity. The ability of individual polymerases to utilize poly dT-oligo dA12-18 as a template-primer at different pH values, ionic strengths and Mg2+-concentrations was also investigated. In comparison to poly dA-oligo dT12-18 template-primer, pol α has 140% of enzyme activity on poly dT-oligo dA12-18 under optimal conditions, whereas the activity of pol ε and pol δ is 4 times and 10 times lower, respectively.
A DNA primase from yeast. Purification and partial characterization.