The PHAT (pseudo-HEAT analogous topology) domain assumes a structure consisting of a layer of three parallel helices packed against a layer of two antiparallel helices, into a cylindrical shaped five-helix bundle. It is found in the RNA-binding protein Smaug, where it is essential for high-affinity RNA binding [1].

1: RNA recognition via the SAM domain of Smaug. Green JB, Gardner CD, Wharton RP, Aggarwal AK; Mol Cell. 2003;11:1537-1548. PMID:12820967