Ca2+ is essential for multistep activation of the heat shock factor in permeabilized cells.

We have developed a novel permeabilized-cell system to study transcription mechanisms. In permeabilized cells, heat-induced activation of the heat shock factor and transcription of the hsp70 gene require Ca2+. Activation involves at least two steps: Ca(2+)- and heat-dependent activation of heat shock factor binding and a second step, prior to transcription of hsp70, that requires ATP and is sensitive to genistein, a protein kinase inhibitor.