16 Posttranscriptional Regulation of Heat Shock Protein Synthesis in Drosophila

Abstract

I. INTRODUCTION
All cells respond to temperatures above their normal growth temperatures by inducing the synthesis of a small group of evolutionarily conserved polypeptides known as the heat shock proteins (hsps). Some of the hsps are required to help cells grow at the upper end of their normal temperature range, others to help cells withstand the toxic effects of more extreme temperatures. Many of the proteins are also produced at normal temperatures or have close relatives that are produced at normal temperatures (the “heat shock cognate” proteins). The hsps and their relatives participate in an extraordinary variety of cellular processes, including DNA synthesis, protein secretion, the response to steroid hormones, and the “chaperoning” of newly synthesized proteins. The variety and complexity of these interactions are only beginning to be unraveled. What defines the hsps as a group, however, is the immediate and very dramatic increase in their synthesis when cells are exposed to higher temperatures (Lindquist and Craig 1988).

Considering the extremely ancient nature of the heat shock response and the extraordinary variety of organisms and cell types in which it is found, it is not surprising that several different mechanisms have evolved to ensure that the hsps will be produced as rapidly as possible after a shift to high temperature. In all organisms investigated, transcriptional regulation plays an important role in the induction of the hsps. In eukaryotes, a heat-shock-activated transcription factor binds to a promoter/enhancer element that provides heat-inducible transcription (for review, see Chapters 17 and 18). In...