A HEAT repeat is a protein tandem repeat structural motif composed of two alpha helices linked by a short loop. HEAT repeats can form alpha solenoids, a type of solenoid protein domain found in a number of cytoplasmic proteins. The name "HEA****T" is an acronym for four proteins in which this repeat structure is found: H untingtin, elongation factor 3 ( E F3), protein phosphatase 2A (PP2 A ), and the yeast kinase T OR1. HEAT repeats form extended superhelical structures which are often involved in intracellular transport; they are structurally related to armadillo repeats. The nuclear transport protein importin beta contains 19 HEAT repeats.

Various HEAT repeat proteins and their structures

Representative examples of HEAT repeat proteins include importin β (also known as karyopherin β) family, regulatory subunits of condensin and cohesin, separase, PIKKs (phosphatidylinositol 3-kinase-related protein kinases) such as ATM (Ataxia telangiectasia mutated) and ATR (Ataxia telangiectasia and Rad3 related), and the microtubule-binding protein XMAP215/Dis1/TOG and CLASP. Thus, cellular functions of HEAT repeat proteins are highly variable. The structure of the following HEAT repeat proteins have been determined so far: