In the fly, there are many genes coding for multiple families of HSPs that function in regulatory pathways, both developmental and the response to heat stress. The developmental regulation is consonant with a role of HSPs as molecular chaperones.
Organisms respond to elevated temperatures by rapidly inducing HSPs.
Thus, HSF responds to the heat shock signal by binding to DNA and regulation of target gene transcriptional competence. Stress induced binding of HSF to DNA is controlled by the transition of HSF from a monomer to a trimer. HSPs may assist in constraining HSF in a latent, monomeric state. When the organism is subjected to heat stress, multiple protein species denature, increasing the demand on HSPs to refold proteins, thereby releasing HSF from cytoplasmic constraint, and allowing its transportation to the nucleus where it undergoes trimerization, and subsequent binding to the promoters of HSPs. Both latent and active forms of HSF interact with hsp70.