Ecdysteroids regulate the synthesis of RNA polymerase molecules in fat body cells ofCalliphora larvae.

In vivo labelling of RNA polymerases I and II with S35-methionine shows that ecdysterone causes a de novo synthesis of both enzymes in nuclei of fat body cells inCalliphora 3rd instar larvae. Binding experiments with H3-α-amanitin demonstrate that the concentration of RNA polymerase II molecules increases two- to threefold within 3 h after ecdysterone treatment. The enhanced polymerase concentration coincides with an enhanced enzymatic activity and an increase in RNA synthesis in response to ecdysteroids.