The effect of ecdysterone on nonhistone proteins in salivary gland chromosomes of Sciara coprophila.

Synthesis and transport of proteins to the cell nucleus during puff induction was studied in S. coprophila. Changes in grain distribution along chromosomes (L-methionine [35S] incorporation into protein) were correlated with puffs induced by ecdysterone in vitro; A pattern of specific labelling at the sites of incipient puffs was noted within 2 h after the addition of the hormone, i.e. grains on the chromosomes were in clusters, characteristic for this time point and not seen in the controls (where only non-specific labeling was noted 0-4 h). Characteristic chromosomal puffs appeared between 3-4 h after the addition of ecdysterone. It was concluded that during ecdysterone-induced puff formation in salivary gland chromosomes, proteins which had been previously synthesized were selectively transported from the cytoplasm to specific sites on the chromosomes.