The isolation and properties of a DNA-directed RNA polymerase from yeast mitochondria

A method is described for the rapid isolation of yeast mitochondrial DNA-directed RNA polymerase. The enzyme obtained had a specific activity of 1.56 nmol UMP incorporated per mg protein in 20 min at 37 degrees C, and is some 95% pure. This purified enzyme upon polyacrylamide gel elctrophoresis consists of a single polypeptide of 68 000 mol. wt. However, the enzyme forms aggregates easily which are affected by ionic strength, an increase decreasing the apparent molecular weight of the aggregates. This property also explains the presence of two peaks of activity upon DEAE-cellulose chromatography. The purified enzyme is still sensitive to rifamycin and to a number of rifamycin derivatives. The enzyme's sensitivity to rifamycin and rifamycin derivatives was compared with Escherichia coli and yeast nuclear RNA polymerases.