Figure 41 Control of mRNA synthesis during transcription of Hsp70. (a) RNA polymerase II pauses after synthesising about 25 nucleotides of the transcript as CHBF binds to HSE. (b) After a heat shock that produces part-denatured proteins heat-shock transcription factor (HSTF) is converted from an inactive into an active DNA-binding form. This occurs in response to the presence of part-denatured proteins. Monomers of HSTF link to form trimers that enter the nucleus. (c) Binding of activated (trimerized) HSTF to the heat-shock regulatory element (HSE) of the promoter of the Hsp70 gene, releases the paused RNA polymerase II, leading to rapid transcription of the Hsp70 gene