Ornithine decarboxylase may function as an initiation factor for RNA polymerase I.

Reparts suggest that the activity of RNA polymerase I is modulated by a labile protein with a hlaf-life of 10 to 20 minutes. Ornithine decarboxylase is the only labile protein (half-life, 10 to 20 minutes) that increases in activity prior to increased RNA polymerase I activity. The addition of a small amount of a highly purified ornithine decarboxylase preparation to an RNA polymerase I assay increases the initial rate of the reaction as well as the time for which the assay is linear. The incorporation patterns of 14C-labeled adenosine triphosphate and 32P-labeled adenosine triphosphate into RNA indicate that the addition of ornithine decarboxylase to the RNA polymerase assay increases the rate of initiation. This report demonstrates a novel way to purify ornithine decarboxylase by RNA polymerase I affinity chromatography and presents data in support of the hypothesis that the labile protein which modulates RNA polymerase I activity is ornithine decarboxylase.