Tritiated-histidine incorporation intoDrosophila salivary chromosomes

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.

Rapidly labeled proteins on the salivary gland chromosomes of Drosophila melanogaster

Experiments on short-term and pulse-chase labeling of chromosome proteins of the salivary glands of Drosophila melanogaster show unique patterns of label in the vicinity of chromosome puffs. A high turnover rate is indicated for these nonhistone proteins, which appear to form a fibrous sheath around the chromosomes. Acrylamide gel analyses of the chromosomal proteins that are quickly labeled, comparing compositions at different stages of development with compositions after heat shock, show that all are different and dependent on which chromosomal puffs are active and producing messenger RNA. The necessity for a continuous and rapid interchange of protein between the nucleus and cytoplasm is indicated, and it appears that regulation of gene activity must be related to this dynamic state of protein exchange. From the technical standpoint, it has been found that scanning electron microscopy (SEM) is especially useful for observing silver grains on opaque autoradiographs. It appears also that SEM will prove useful in a variety of studies of chromosome structure.