[5] STI1 belongs to the large group of co-chaperones, which regulate and assist the major chaperones (mainly heat shock proteins).

It was first discovered in yeast and homologues were identified in humans, mice, rats, insects, plants, parasites, and viruses.

STI proteins are characterized by some structural features: All homologues have nine tetratricopeptide repeat (TPR) motifs, that are clustered into domains of three TPRs.

The intermediate structures of heat shock machinery are difficult to characterize completely because of the transient and fast paced nature of chaperone function.

In Drosophila RNA interference pathways, Hop has been shown to be an integral part of the pre-RISC complex for siRNAs.