RNA polymerase activities of Calliphora vicina larvae in response to ecdysteroids

Abstract The effect of ecdysterone on RNA polymerase activities, partially purified from fat body nuclei of Calliphora vicina third instar larvae, has been investigated. Three different forms of DNA-dependent RNA polymerase activities have been isolated and resolved on the basis of chromatographic behaviour and α-amanitin sensitivity. RNA polymerase I and II are similar to the analogous polymerases from other eukaryotic organisms in their enzymatic properties, such as salt and metal-ion optima and in their DNA requirements. The activities of polymerase I and II could be correlated with the endogenous ecdysteroid concentrations of third instars. The enzyme activities increase two-fold in white puparia compared to five-day-old larvae. After injection of ecdysterone in five-day-old larvae the enzyme activities are stimulated within 3 hr to the same amount as in white puparia. The enzyme stimulation coincides with the increase in RNA synthesis. Our results indicate the existence of a hormone dependent mechanism for regulating the intracellular activities of RNA polymerases I and II.