Figure 2. Members of the mammalian HSF family.

a | A phylogenetic tree showing the species-specific relationship of heat shock factors (HSFs) among higher eukaryotes. Two recently found, but still poorly characterized, family members are: HSFY, which is located on the human Y chromosome and on the murine chromosome 2 (HSFY2), and HSFX, which has only been found on the human X chromosome^144–146. HSFY and HSFX exist in two identical copies on their respective chromosome. The phylogenetic tree was generated in CLUSTAL W¹⁴⁷ and gaps were excluded from all phylogenetic analyses. The numbers represent bootstrap values (1000 bootstrap replicates were carried out). b | A schematic of the functional domains of the human and murine HSF family members. The conserved domains of distinct HSFs are indicated: the DNA-binding domain (DBD), the oligomerization domain (heptad repeat A (HR-A) and HR-B) and the carboxy-terminal HR-C. All HSFs contain the characteristic helix-loop-helix DBD. HSF1–HSF4 contain Leu zipper-like HR domains, which are required for homotrimerization or heterotrimerization. Yeast Hsf is included as a comparison. Image in part a is modified, with permission, from REF. 10 © (2010) The American Society for Cell Biology.