8 The Function and Regulation of Heat Shock Proteins in Escherichia coli

Abstract

I. INTRODUCTION
The heat shock response in E. coli was first identified by monitoring the response of individual proteins to temperature upshift (Lemaux et al. 1978; Yamamori et al. 1978; for review, see Neidhardt and VanBogelen 1987). Most E. coli proteins do not change their rate of synthesis significantly when the temperature is suddenly increased. However, a small group of proteins show a large but transient increase in their rate of synthesis. These proteins have been called the heat shock proteins (hsps). hsps are induced by several stimuli other than heat, including DNA-damaging agents, coumermycin, amino acid analogs, starvation for amino acids, bacteriophage λ infection, and ethanol. hsps may serve to protect the cell against a variety of adverse conditions.

The heat shock regulon includes about 20 of the approximately 2000 proteins that E. coli synthesizes (Neidhardt and VanBogelen 1987). Two of the major E. coli hsps are homologous to eukaryotic hsps. DnaK is homologous to the eukaryotic hsp70 family (Bardwell and Craig 1984), and GroEL is related to eukaryotic mitochondrial hsps (McMullin and Hallberg 1988), as well as the plant RuBisCO binding protein (Hemmingsen et al. 1988). HptG, another E. coli hsp, is homologous to hsp83 (Bardwell and Craig 1987). This conservation of hsps suggests that the functions required to protect the cell from thermal stress are evolutionarily conserved among nearly all organisms. Thus, a study of the function of the E. coli hsps will not only contribute to an understanding of the physiology of eubacteria, but will also...