Relationship of ornithine decarboxylase to RNA polymerase I activity

Ornithine decarboxylase activity can be rapidly elevated 50- to 100-fold by the administration of methylxanthine derivatives such as methylisobutylxanthine. This elevation occurs just prior to the increase in RNA polymerase I activity. Inhibitors of RNA synthesis and of protein synthesis suggest that any alteration in the ornithine decarboxylase response results in a similar alteration in the level of α-amanitin-insensitive RNA polymerase. Addition of a partially purified ornithine decarboxylase preparation to the RNA polymerase assay increased both the initial rate of ³H-UTP incorporation and the length of time that the polymerase assay was linear. It is suggested that ornithine decarboxylase is the labile protein that modulates the level of RNA polymerase I.