9.A.60 The Small Nuclear RNA Exporter (snRNA-E) Family

Phosphorylated adaptor for RNA export (PHAX) (phosphorylated in the nucleus, dephosphorylated in the cytoplasm) is the key export mediator for spliceosomal U small nuclear RNA (snRNA) precursors in metazoa. PHAX is enriched in Cajal bodies (CBs), nuclear subdomains involved in the biogenesis of small ribonucleoproteins. Suzuki et al. (2010) showed that U snRNA precursors microinjected into Xenopus laevis oocyte nuclei temporarily concentrate in CBs but gradually decrease as RNA export proceeds. Inhibition of PHAX activity in a dominant-negative PHAX mutant inhibits U snRNA export and simultaneously enhances accumulation of U snRNA precursors in CBs, indicating that U snRNA binding to PHAX is required for efficient exit of U snRNAs from CBs. Similar results were obtained with U snRNAs transcribed from microinjected genes (Suzuki et al., 2010).



Suzuki, T., H. Izumi, and M. Ohno. (2010). Cajal body surveillance of U snRNA export complex assembly. J. Cell Biol. 190: 603-612.


TC#NameOrganismal TypeExample

The U snRNA export complex including: phosphorylated adaptor for RNA export (PHAX/RNUXA), nuclear cap-binding protein-1/2 (NCBP1/NCBP2), and RAN GTPase (see also 9.A.50).


U snRNA export complex of Homo sapiens 
(1) Phosphorylated adaptor for RNA export c(PHAX/RNUXA) (Q9H814)
(2) Nuclear cap-binding protein-1, NCBP1 (Q09161)
(3) Nuclear cap-binding protein-2, NCBP2 (P52298)
(4) RAN GTPase (see also 9.A.50) (P62826)