17 Regulation of Heat Shock Gene Transcription by a Family of Heat Shock Factors

Abstract

I. INTRODUCTION All bacterial, plant, and animal cells must cope with rapid changes in their environment, including exposure to elevated temperatures, heavy metals, toxins, oxidants, and bacterial and viral infection, by a rapid and often dramatic change in the patterns of gene expression, resulting in the elevated synthesis of a family of heat shock proteins and molecular chaperones (Lindquist and Craig 1988; Morimoto et al. 1990). Heat shock proteins ensure survival under stressful conditions, which if left unchecked, lead to irreversible cell damage and untimely cell death. They have essential roles in protein biosynthesis, specifically in the synthesis, transport, and translocation of proteins and in the regulation of protein conformation, and are also referred to as molecular chaperones (Craig et al.; Langer and Neupert; Brodsky and Schekman; Gething et al.; Dice et al.; Hightower et al.; Georgopoulos et al.; Frydman and Hartl; Randall et al.; Willison and Kuboda; Bohen and Yamamoto; all this volume). Heat shock proteins constitute a surprisingly large fraction of the protein within a cell, amounting to 5–10% of the total protein mass in cells growing under ambient conditions. Yet, despite their abundance, the genes encoding heat shock proteins are rapidly induced in response to stressful conditions. The consequence of this genetic switch, which is activated in response to a perturbation of the physiological state of the cell, is the elevated expression of constitutively expressed heat shock proteins and the de novo induction of heat shock genes that are expressed primarily in response to stress. A...