Heat shock protein GroE of Escherichia coli: key protective roles against thermal stress.

Abstract

An Escbericbia coli mutant lacking the heat shock a-factor (o^^) is defective in transcription from heat shock promoters and cannot grow at temperatures above 20°C. To assess physiological roles of a^^ and heat shock proteins, we isolated and characterized a set of temperature-resistant revertants from this deletion (^rpoH) mutant. Most of them were found to carry a DNA insertion in the groE upstream region, resulting in high-level synthesis of major heat shock proteins GroE (GroES and GroEL). The levels of GroE produced varied in different revertants and correlated well with the maximum permissive temperatures; the highest GroE producers (-10% of total protein) grew up to 40°C but not at 42°C. An additional mutation causing hyperproduction of DnaK (hsp70 homolog) was required for growth at 42°C. Such effects of GroE and DnaK on the a^^-deletion strains were also confirmed by using multicopy plasmids carrying groE or dnaK. Thus, GroE plays a key protective role in supporting growth at normal physiological temperatures (20-40°C), whereas high levels of DnaK are required primarily at higher temperature.

Heat Shock Proteins hsp60 and hsp70: Their Roles in Folding, Assembly and Membrane Translocation of Proteins

“…The actual level of GroE proteins can determine the maximal growth temperature (KUSUKAWA and YURA 1988). This suggests a more general role of the GroE proteins for cell function.…”

Heat‐shock proteins as molecular chaperones

“…Both have reduced levels of RNA and DNA synthesis, and both are required for bacteriophage morphogenesis. Both mutants show increased proteolysis (Georgopoulos et al, 1991) and both are implicated in the maintenance of secretory precursors in a transport-competent state (Bochkareva et al, 1988;Lecker et al, 1989;Wild et al, 1992) but only DnaK is required for thennotolerance (KUSUkawa and Yura, 1988). GroEL binds to partially unfolded proteins in a ratio of 1 : 1 or 1 : 2 of oligomers to unfolded polypeptide and has been demonstrated to mediate the refolding and assembly of a variety of enzymes denatured in vitro using urea guanidinium or heat.…”

Purification, cDNA cloning and Northern‐blot analysis of mitochondrial chaperonin 60 from pumpkin cotyledons

“…Therefore, it is of interest to determine whether or not levels of mRNA species for mitochondrial Cpn60 in higher plants are also increased not only by heat shock but also by other stresses or plant hormones. Chaperonins are essential for cell viability in E. coli [40] and yeast [lo] and seem to play a key role in thermotolerance, at least in E. coli [19]. Thus, it seems likely that mitochondrial Cpn6O may play a key role in mitochondrial biogenesis and adaptation to stresses such as a heat shock.…”

“…Many molecular chaperones were at first identified as proteins induced by stresses such as a heat shock [14]. In fact, levels of groE protcins increase dramatically upon heat shock and they play a key role in thermotolerance in E. coli [19]. Furthermore, a 104-kDa heat-shock protein, hspl04, is vital for tolerance to heat, ethanol and other stresses in yeast 120, 211.…”