Abstract: The exposure of cells, tissues and organs to “stress,” such as elevated temperature, stimulates production of active heat stress transcription factors (HSF), which in turn, induce expression of genes regulated by stress promoters. Normally, the activity of stress promoters declines after cells, tissues and organs are returned to a normal condition. Mutant forms of HSF, however, can constitutively transactivate stress genes, in the absence of stress. By taking advantage of such mutant HSF, molecular circuits can be devised to provide a sustained expression of a gene of interest using a single application of stress.