Abstract
A temperature-sensitive ras allele has an effective lethal phase at 29 degrees C about 12 hr after pupation and a temperature-sensitive period for lethality beginning midway through the third larval instar and ending around pupation. The mutation also alters the quantity of pteridines present in the eyes, testes, and Malpighian tubules at 29 degrees C. The temperature-sensitive period for pigment production in the Malpighian tubules occurs in the egg and first instar larvae, and in eyes and testes after pupation. The demonstrated autonomy of the mutant in the eyes implies the tissue-specific functioning of the gene. We suggest that the different temperature-sensitive periods for a single mutation indicate tissue-specific activation of a gene at different times during development, although the possibility of activation of preformed polypeptides has not been eliminated.
