3H-uridine incorporation in the puff 93D and in chromocentric heterochromatin of heat shocked salivary glands of Drosophila melanogaster.

The autoradiographic patterns of 3H-uridine labelling of the major temperature shock puff sites and the chromocentric (beta-)heterochromatin in heat shocked (37 degrees C) salivary glands of Drosophila melanogaster have been studied. It is seen that in response to the heat shock treatment, four of the major temperature shock puffs (63BC, 87A, 87C and 95D) show a correlated level of 3H-uridine incorporation in a given nucleus. However, although the mean grain density on 93D puff is maximum in the heat shocked preparations, in individual nuclei this puff is labelled to a widely varying level and this variation in its labelling is statistically not correlated to the labelling of the other four temperature shock puffs in a nucleus. The chromocentric beta-heterochromatin, which has been shown in several earlier studies to hybridize with temperature shock RNA fractions, is seen to be totally inactive in transcription after the heat shock.