Purification and properties of two RNA polymerases from Physarum polycephalum.

Two RNA polymerases have been purified from the slime mold Physarum polycephalum, one sensitive and one resistant to alpha-amanitin. Both enzymes are more active with denatured DNA than native DNA as a template and prefer Mn(++) rather than Mg(++) as a divalent cation. The alpha-amanitin-sensitive enzyme shows maximum activity at 0.15 M KCl, whereas the resistant enzyme is most active at very low ionic strength. Analysis of the resistant enzyme on polyacrylamide gels containing sodium dodecyl sulfate shows two subunits present in a 1:1 ratio with molecular weights of 205,000 and 125,000.