20-Hydroxyecdysone stimulates RNA polymerase I activity in silkmoth wing epidermis by increased synthesis and phosphorylation

Abstract

The activities of RNA polymerases I and II in the wing epidermis of dispausing silkmoth pupae increased about tenfold during the first day after administration of either 20-hydroxyecdysone (20E) or 20E plus juvenile hormone (Katula et al., 1981a). The aim of these studies was to correlate these increases in RNA polymerase I and II activities to their amounts in hormone stimulated wing epidermis. The enzyme activities were measured by standard procedures while their amounts were determined by the application of a modified ELISA with subunit-specific monoclonal antibodies. Results showed that the increase in the amount of RNA polymerase I during the first 24 h accounted for only about 60% of the increase in activity. Alkaline phosphatase decreased the activity of the newly synthesized enzyme by 40–50%. These results indicate that hormone-stimulation of RNA polymerase I activity is due to a combination of synthesis of the enzyme and phosphorylation of the enzyme and/or tightly associated factors. RNA polymerases II and III determined by differential ELISA using a monoclonal antibody specific to a common subunit followed developmental changes similar to those of RNA polymerase I. The amounts and activity of the enzymes during the first 48 h were similar in wing tissue that followed the second pupal development (20E + juvenile hormone) compared to tissue that developed into adult wings (20E).