A DNA Polymerase from Ustilago maydis

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Abstract
A DNA polymerase from U. maydis was purified to apparent homogeneity. The native enzyme possesses a subunit structure consisting of 50,000 and 55,000-dalton monomers. The apparent sedimentation coefficient of the polymerase activity in the absence of salt is 8.4 S (Mr = 180,000-200,000), that in its presence (0.6 M NaCl or 0.12 M KCl) being 6.3 S (Mr = 80,000-100,000). Low concentrations of EDTA also converted the 8.4-S to a 6.3-S form, whereas Mg ions catalyzed the reverse association. The enzyme has an absolute requirement for both a DNA or RNA template and a DNA primer. For homopolymer templates the primer requirement was satisfied by a short complementary oligodeoxynucleotide, but oligoribonucleotides were extremely inefficient primers. With the template-primer poly(dA).cntdot.(dT)12, the enzyme added an average of 50 dTMP nucleotides on to each primer molecule, whereas with poly(rA).cntdot.(dT)12, this figure was 300. The enzyme also possesses an associated DNase activity. No other DNA polymerase activity was detected in cell-free extracts of U. maydis.