The Biological Role of the Universally Conserved E. coli Heat Shock Proteins

The heat shock or stress response has been universally conserved among organisms (reviewed in Morimoto et al., 1990; Georgopoulos et al., 1990; Gross et al., 1990). When the gram-negative bacterium, E. coli is treated with a heat shock, the cell responds by transiently accelerating the rate of transcription of heat shock genes. This increased transcription is promoted by the Eσ32 RNA polymerase holoenzyme. The genes of approximately half of the 20 or so observed heat shock proteins in E. coli have been cloned and their corresponding proteins purified and characterized. Surprisingly, five of the major heat shock genes, namely dnaK, dnaJ, grpE, groES, and groEL, were previously identified because certain mutations in them block bacteriophage λ growth (reviewed in Friedman et al., 1984; Georgopoulos et al., 1990). The dnaK, dnaJ, and grpE gene products are required for bacteriophage λ growth specifically at the level of DNA replication, whereas the groES and groEL gene products are required specifically at the level of prohead assembly. In this paper, we summarize our previous and current studies on these five genes and suggest models for the mechanism of action of their gene products.