Puffs appear and disappear on Drosophila salivary gland polytene chromosomes at specific developmental timepoints or in response to external stimuli. This thesis is an analysis of the functions and regulation of three RNAs transcribed from the puff at 68C on the left arm of the third chromosome.
The nucleotide sequence of the DNA encoding these RNAs was used to predict the physical and chemical properties expected of their protein products. Analysis of radiolabeled salivary glands revealed polypeptides having the characteristics predicted for the products of the 68C RNAs. Amino acid sequencing of these proteins showed that they are in fact encoded by the 68C RNAs. All three polypeptides were found to be part of the salivary gland glue: one is the previously described sgs-3, the others the newly identified glue proteins sgs-7 and sgs-8.
The effect of the steroid hormone ecdysterone on the 68C RNAs was examined by culturing salivary glands in vitro in the presence or absence of the hormone. The presence of the steroid caused the RNAs to disappear more rapidly than they would in its absence. Pulse-labeling experiments demonstrated that the effect of ecdysterone is on an early step in RNA production, probably transcription. The effect on the 68C RNAs is very rapid, more rapid than puff regression. The three RNAs appear to be coordinately regulated.
The expression of glue protein genes in a non-pupariating mutant strain of Drosophila has been studied. Although a puff is present at position 68C on the third chromosome in the mutants, the Sgs-3, Sgs-7 and Sgs-8 genes are not expressed. Pulse-labeling experiments indicate that the mutation affects transcription of these genes. Other researchers have mapped the non-pupariating mutation to position 2B on the X chromosome. It appears that a product of a gene at 2B or a product whose synthesis is induced by a gene at 2B is necessary for transcription of the 68C glue protein genes. This trans-acting regulatory element produces its effect by interacting with DNA sequences within or very close to the glue genes at 68C. These results along with transcription autoradiograms show that the puff at 68C is not caused by transcription of Sgs-3, Sgs-7, Sgs-8 or anyother genes located within the puff region.
