Steroid and high-temperature induction of the small heat-shock protein genes in Drosophila.
Transcription of the four small heat-shock protein genes of Drosophila melanogaster can be induced in cultured cells by high-temperature shock, or by physiological doses of the moulting hormone, ecdysterone. We have characterized and compared the two induction events, focusing on hsp22 and hsp23, in terms of rates of heat-shock protein synthesis, transcription rate, messenger RNA abundance and mRNA half-life. The results indicate that relative to hsp22, the rate of hsp23 synthesis is significantly greater during recovery from heat shock and during ecdysterone induction. This difference is not due to differences in transcription rate, but rather reflects differences in mRNA stability and translational efficiency. One intriguing finding is that hsp message stability is temperature-dependent; hsp transcripts are two to three times more stable at 35 degrees C than at 25 degrees C. The possible mechanism and significance of this phenomenon are discussed.
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