RNA and protein synthesis in the cellular response to a hormone, ecdysone.

Abstract

Evidence has accumulated in the past few years indicating that changes in RNA and protein syntheses are among the first responses of cells to many, if not to all, hormones (see refs. 1 and 2 for reviews).The mechanism(s) which provoke these changes, their interrelationships, and their relationship to other cellular responses to the respective hormones, however, are still a matter of conjecture.The present communication deals with the effect of inhibitors of RNA [actino- mycin D3] and protein synthesis [cycloheximide4' 5] on the response of Chironomus salivary gland cells to the insect molting hormone, ecdysone.In these cells, changes in RNA metabolism following hormone treatment are indicated by changes in the pattern of puffing in their giant chromosomes.6-8Chromosomal loci which respond to the hormone do so in a regular sequence: the first puffs appear within less than an hour after a hormone injection, the last ones after 3-4 days.6One might expect that the activity of these loci is controlled by the hormone with dif- erent immediacy, i.e., via various numbers of intermediate steps.9The experi- ments to be reported here were undertaken to examine this hypothesis.The results obtained indicate that induction of RNA synthesis at specific chro- mosomal loci by ecdysone is independent of protein synthesis, and consequently suggest that this hormonal effect on transcription is not preceded by an effect on translation.All subsequent activations of RNA synthesis at other chromosomal loci, on the other hand, depend on preceding RNA and protein synthesis.