Heat stress nGaannTTCnnGAAn⊥DNA Heat shock element HSP70 Heat shock protein mRNA ∩QQ Heat factor (HSF) Heat shock F oteins Igure (HSP) FIGURE 25. 11 The heat shock factor(HSF)cycle activates leading to the translation of HSPs among which are HSP70 the synthesis of heat shock protein mRNAs In nonstressed (4). The HSF trimers associated with the HSE are phospho- cells, HSF normally exists in a monomeric state()associ- rylated (5) facilitating the binding of HSP70 to the phos- ated with HSP70 proteins. Upon the onset of an episode of phorylated trimers(6). The HSP70 trimer complex(7)disso- heat stress, HSP70 dissociates from HSF which subse- ciates from the HSE and disassembles and dephosphory quently trimerizes(2). Active trimers bind to heat shock lates into HSF monomers(8), which subsequently bind HSP elements(HSE)in the promoter of heat shock protein(HSP) reforming the resting HSP70/HSF complex (After Bray et genes(3), and activate the transcription of HSP mRNAs al.2000.)Figure 13-6