The vertebrate Tap protein is a member of the NXF family of shuttling transport receptors for nuclear export of mRNA. Tap has a modular structure, and its most C-terminal domain is important for binding to FG repeat-containing nuclear pore proteins (FG-nucleoporins) and is sufficient to mediate nuclear shuttling [1]. The structure of the C-terminal domain is composed of four helices [1]. The structure is related to the UBA domain.

1: Structure of the C-terminal FG-nucleoporin binding domain of Tap/NXF1. Grant RP, Hurt E, Neuhaus D, Stewart M; Nat Struct Biol 2002;9:247-251. PMID:11875519