Heat shock proteins (HSPs) are a family of highly conserved stress response proteins. Heat shock proteins function primarily as molecular chaperones by facilitating the folding of other cellular proteins, preventing protein aggregation or targeting improperly folded proteins to specific degradative pathways. HSPs are typically expressed at low levels under normal physiological conditions, but are dramatically up-regulated in response to cellular stress. HSP70 (also known as HSPA1A, HSP70-1, and HSP72) is a 72 kDa member of the heat shock protein 70 family of proteins. HSP70 is required to target some misfolded proteins to the ubiquitin E3 ligase CHIP (also known as Stub1) for subsequent ubiquitination.