The heat shock transcription factor (HSF) is a trimer that binds to DNA containing inverted repeats of the sequence nGAAn. HSF can bind DNA with the sequence nGAAnnTTCn or with the sequence nTTCnnGAAn, with little preference for either sequence over the other. However, (nGAAnnTTCn)2 is considerably less active as a heat shock response element (HSE) than is (nTTCnnGAAn)2. The electrophoretic mobilities of DNA-protein complexes and chemical cross-linking between protein monomers indicate that the sequence (nGAAnnTTCn)2 is capable of binding a single HSF trimer. In contrast, the sequence with higher biological activity, (nTTCnnGAAn)2, is capable of binding two trimers. Thus, the ability of four-nGAAn-element HSEs to bind one or two trimers depends on the permutation with which the elements are presented. A survey of naturally occurring HSEs shows the sequence (nTTCnnGAAn)2 to be the more prevalent. We suggest that the greater ability of one permutation over the other to bind two HSF trimers accounts for the initial identification of the naturall occurring heat shock consensus sequence as a region of dyad symmetry.The eukaryotic heat shock transcription factor (HSF) is the main transcription factor responsible for expression of heat shock protein (hsp) genes during periods of stress. The activity of HSF is exquisitely sensitive to the presence of unfolded, denatured, or aberrant proteins, which appear to act as an intracellular signal to induce hsp gene transcription. It is likely that this signal acts on the posttranslational regulation of HSF activity, at least in part, through one of the heat shock proteins, hsp7O (reviewed in reference 16). Association of hsp70 with HSF appears to be necessary to sequester HSF in a form that is unable to activate transcription effectively. Any stress-induced increase in the concentration of aberrant proteins is thought to result in the titration of hsp70 and the accumulation of HSF in an active form.In vertebrate and Drosophila cells, the inactive form of HSF is a non-DNA-binding monomer (5,20,29). Heat shock causes the assembly of HSF monomers into trimers, which are then competent to bind DNA (5,20,29). In the yeast Saccharomyces cerevisiae, HSF is constitutively competent to bind DNA (11) and is trimeric even before heat shock (25).The observation that HSF is trimeric raises some interesting questions with regard to its DNA interaction. The initial analyses of natural heat shock elements (HSEs) resulted in the description of a consensus sequence, CTnGAAnnTTC nAG (17,18,27). This consensus HSE is palindromic, reminiscent of binding sites for dimeric proteins. It has more recently been suggested that functional HSEs are more properly described as inverted repeats of the sequence module nGAAn (2, 31). Within an array of nGAAn repeats, it is likely that each nGAAn element is contacted by a single HSF monomer; Perisic et al. (19) observed that repeats of two to three nGAAn elements are bound by a single trimer of Drosophila HSF, repeats of four to six elements are bound by two tri...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.