protein-stimulated activity, temperature sensitivity and heat stability of the ATPase activity of native Hsc70 purified from G. mirabilis white muscle. Similar to other chaperones in the 70 kDa heat-shock protein family, G. mirabilis Hsc70 exhibited a low intrinsic ATPase activity

as a dominant environmental factor and has been shown to influence biological systems at numerous levels of organization (Cossins and Bowler, 1987; Johnston and Bennett, 1996). The pervasive effects of temperature on living systems range from influencing the biogeographical distribution of ectothermic organisms (Hubbs, 1948; Fields et al., 1993; Marko, 1998; Sanford, 1999) to influencing the structure and function of proteins (for a review, see Somero, 1995). In the latter category, the temperature interactions of certain proteins, particularly enzymes, have received a great deal of attention in comparative biochemistry (e.g. Graves and Somero, 1982; McFall-Ngai and Horwitz, 1990; Dahlhoff and Somero, 1993; Fields and Somero, 1997; Holland et al., 1997; Jaenicke and Bohm, 1998). However, one important class of proteins, the molecular chaperones, has gone largely unstudied. The basic action of molecular chaperones is to recognize and bind selectively to unfolded, non-native proteins in a cell (for reviews, see Fink, 1999; Saibil, 2000). As such, molecular chaperones have a central role in the process of protein biosynthesis, and the temperature interactions of molecular chaperones therefore have significant biological consequences for organisms synthesizing proteins in variable-temperature environments. The larger goal of this study was to begin to characterize the relationship between temperature and molecular chaperone function as it occurs in ectothermic animals under environmentally relevant temperatures. Although very little is known about the temperature relationships of molecular chaperones in ectotherms in natural populations, a great deal is known about the cellular role and biochemistry of the molecular chaperones in general (for reviews, see Hartl, 1996; Gething, 1997; Morimoto, 1998; Fink, 1999; Feder and Hofmann, 1999; Bukau, 1999). Molecular chaperones are ubiquitous and have been found in virtually every organism examined (Lindquist, 1986). The major classes of molecular chaperones include the six families 2675 The Journal of Experimental Biology 204, 2675–2682 (2001) Printed in Great Britain © The Company of Biologists Limited 2001 JEB3354