The phosphorylated adaptor for RNA export (PHAX) protein transports U3 snoRNA from the nucleus after transcription [1, 2]. This entry represents the highly conserved U3 snoRNA-binding domain of PHAX, which is characterised by having two pairs of adjacent glycines with the sequence motif GGx12GG. This domain adopts a novel helical fold and binds non-specific single-stranded RNA and comprises five alpha-helices linked by short loops containing 1 to 4 residues, apart from helices alpha3 and 4 that are linked by 13 residues. The fold is unique to this kind of RNA binding domains which show no structural homology with other RNA-binding domains [2].

1: The evolutionarily conserved region of the U snRNA export mediator PHAX is a novel RNA-binding domain that is essential for U snRNA export. Segref A, Mattaj IW, Ohno M; RNA. 2001;7:351-360. PMID:11333016

2: Structure and RNA recognition by the snRNA and snoRNA transport factor PHAX. Mourao A, Varrot A, Mackereth CD, Cusack S, Sattler M; RNA. 2010;16:1205-1216. PMID:20430857