Thermotolerant desert lizards characteristically differ in terms of heat-shock system regulation

We compare the properties and activation of heat-shock transcription factor (HSF1) and the synthesis of a major family of heat-shock proteins (HSP70) in lizard species inhabiting ecological niches with strikingly different th ermal parameters. Under normal non-heat-shock conditions, all desert-dwelli ng lizard species studied so far differ from a northern, non-desert species (Lacerta vivipara) in the electrophoretic mobility and content of proteins constitutively bound to the regulatory heat-shock elements in the heat-sho ck gene promoter. Under these conditions, levels of activated HSF1 and of b oth HSP70 mRNA and protein are higher in the desert species than in the non -desert species. Upon heat shock, HSF1 aggregates in all species studied, a lthough in desert species HSF1 subsequently disaggregates more rapidly, Cel ls of the northern species have a lower thermal threshold for HSP expressio n than those of the desert species, which correlates with the relatively lo w constitutive level of HSPs and high basal content of HSF1 in their cells.