Fine Tuning of the HSR in Various Organisms

Abstract

It is widely assumed that heat shock response system in eukaryotes is amazingly conserved. Thus, all described organisms possess one or several genes encoding transcription factors belonging to HSF family that recognize the same sequences (HSEs) in the promoters of various Hsps genes (Åkerfelt et al. 2010; Morimoto 1998; Wu 1995). Furthermore, HSF family members in different organisms contain two highly similar domains responsible for DNA-binding and heat-induced trimerization as described in detail in Chap. 3. HSF recognizes practically the same simple sequences within promoters of Hsp genes (GAANNTTCNNGAA) that usually present in several copies at a regular distance from the transcription start. Various lines of evidence demonstrated that Hsp70 gene promoter is able to efficiently function in the cells of phylogenetically distant organisms even belonging to different phyla. Thus, reporter constructs under the control of Drosophila melanogaster Hsp70 gene promoter were readily expressed in the cells of mosquito Aedes aegypti, silkworm Bombix mori transgenic strains and in sea urchin embryos (Berger et al. 1985; McMahon et al. 1984; Uhlirova et al. 2002). Furthermore, constructs with D. melanogaster Hsp70 regulatory region were efficiently transcribed in Xenopus oocytes, rat fibroblasts and monkey COS cells (Bienz and Pelham 1982; Burke and Ish-Horowicz 1982; Mirault et al. 1982; Voellmy and Rungger 1982). Importantly, all such constructs exhibited clear-cut heat-inducible pattern of expression in the cells of the foreign hosts, thus corroborating the presumed high conservatism of HS response in unrelated organisms.