Members of this family are involved in mediating U snRNA export from the nucleus. They adopt a highly helical structure, wherein the polypeptide chain forms a right-handed solenoid. At the tertiary level, the domain is composed of a superhelical arrangement of successive antiparallel pairs of helices [1].

1: Crystal structure of the human nuclear cap binding complex. Mazza C, Ohno M, Segref A, Mattaj IW, Cusack S; Mol Cell. 2001;8:383-396. PMID:11545740