Figure 1.

(A) Leucine zippers are thought to repress HSF1 activity and facilitate HSF1 homotrimerization via coiled-coil interactions. (B) Screen used to identify constitutively trimerized alleles of human HSF1. A yeast plasmid expressing human HSF1 was transformed into mutagenic XL-1 Red E. coli to generate a library of mutant HSF1 plasmids that was transformed into a yeast strain with a conditionally expressed yeast HSF allele. Constitutively trimerized human HSF1 alleles were selected by growth on dextrose containing medium, which extinguishes expression of yeast HSF, and identified by DNA sequencing.