Effect of insect hormones on RNA polymerases of mass-isolated imaginal discs of Drosophila melanogaster cultured in vitro.

Four chromatographically separable DNA-dependent RNA polymerases (nucleosidetriphosphate:RNA nucleotidyltransferase; EC 2.7.7.6) were partially purified from imaginal discs of Drosophila melanogaster. Their properties are similar to those described for RNA polymerases I and II isolated from other eukaryotes. In vitro incubation of discs with beta-ecdysone, juvenile hormone, or cycloheximide resulted in increased activity of RNA polymerase I. The increase was irreversible with beta-ecdysone incubation and removal but reversible with juvenile hormone incubation and removal. With beta-ecdysone, the rate of the increase in polymerase I activity paralleled the kinetics of ecdysone binding to discs and increases in the rate of precursor incorporation into RNA. A model to explain the increased acticity of RNA polymerase I is presented.