A DNA-DEPENDENT RNA-SYNTHESIS BY WHEAT-GERM RNA POLYMERASE-II INSENSITIVE TO THE FUNGAL TOXIN ALPHA-AMANITIN

Wheat-germ RNA polymerase II is able to catalyse a DNA-dependent reaction of RNA synthesis in the presence of a high concentration (1 mg/ml) of the fungal toxin a-amanitin. This anomalous reaction is specifically directed by single-stranded or double-stranded homopolymer templates, such as poly(dC) or poly(dC) . poly(dG), and occurs in the presence of either Mn2+ or Mg2+ as the bivalent metal cofactor. In contrast, the transcription of other synthetic templates, such as poly(dT), poly(dA) . poly(dT) or poly[d(A-T)] is completely abolished in the presence of 1-mu-g of alpha-amanitin/ml, in agreement with well-established biochemical properties of class II RNA polymerases. Size analysis of reaction products resulting from transcription of (dC)n templates of defined lengths suggests that polymerization of RNA chains proceeds through a slippage mechanism. The fact that alpha-amanitin does not impede this synthetic reaction implies that the amatoxin interferes with the translocation of wheat-germ RNA polymerase II along the DNA template.