ABSTRACT
1. Fourth-instar larvae of Rhynchosciara americana were injected with the insect molting hormone, ecdysterone, giving final hemolymph concentrations from 4.46 to 223µM. 2. Induction of the DNA puff, B2b, in the proximal (S1) region of the salivary glands of Rhynchosciara americana by 22.6 µM ecdyesterone, was accompanied by the production of an mRNA and a polypeptide with the same characteristics as B2b products produced during normal development. This mRNA and polypeptide were restricted to the proximal region of the gland, as is the B2b puff. 3. Synthesis of other poly (A) +RNAs was also stimulated in S1 by ecdysterone, and other puffs that appear during normal development were induced. However, rRNA production in S1 goes through a pattern of inhibition, followed by recovery when B2b is puffed, and subsequent inhibition. 4. Low molecular weight RNA, with a peak in the region of 4S, is stimulated after ecdysterone administration