HEAT, type 2 <p>The HEAT repeat is a tandemly repeated, 37-47 amino acid long moduleoccurring in a number of cytoplasmic proteins, including the fourname-giving proteins huntingtin, elongation factor 3 (EF3), the 65 Kdalpha regulatory subunit of protein phosphatase 2A (PP2A) and theyeast PI3-kinase TOR1 [<cite idref="PUB00006179"/>]. Arrays of HEAT repeats consists of 3 to 36units forming a rod-like helical structure and appear to function as protein-protein interaction surfaces. It has been noted that manyHEAT repeat-containing proteins are involved in intracellular transport processes.</p><p>In the crystal structure of PP2A PR65/A [<cite idref="PUB00006180"/>], the HEAT repeats consistof pairs of antiparallel alpha helices [<cite idref="PUB00006179"/>].</p>