Structural highlights
Function
[PHAX_HUMAN] A phosphoprotein adapter involved in the XPO1-mediated U snRNA export from the nucleus. Bridge components required for U snRNA export, the cap binding complex (CBC)-bound snRNA on the one hand and the GTPase Ran in its active GTP-bound form together with the export receptor XPO1 on the other. Its phosphorylation in the nucleus is required for U snRNA export complex assembly and export, while its dephosphorylation in the cytoplasm causes export complex disassembly. It is recycled back to the nucleus via the importin alpha/beta heterodimeric import receptor. The directionality of nuclear export is thought to be conferred by an asymmetric distribution of the GTP- and GDP-bound forms of Ran between the cytoplasm and nucleus. Its compartmentalized phosphorylation cycle may also contribute to the directionality of export. Binds strongly to m7G-capped U1 and U5 small nuclear RNAs (snRNAs) in a sequence-unspecific manner and phosphorylation-independent manner (By similarity). Plays also a role in the biogenesis of U3 small nucleolar RNA (snoRNA). Involved in the U3 snoRNA transport from nucleoplasm to Cajal bodies. Binds strongly to m7G-capped U3, U8 and U13 precursor snoRNAs and weakly to trimethylated (TMG)-capped U3, U8 and U13 snoRNAs. Binds also to telomerase RNA.[1] [2]
Evolutionary Conservation
Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.
Publication Abstract from PubMed
Small nuclear and small nucleolar RNAs (snRNAs and snoRNAs) are critical components of snRNPs and snoRNPs and play an essential role in the maturation of, respectively, mRNAs and rRNAs within the nucleus of eukaryotic cells. Complex and specific pathways exist for the assembly of snRNPs and snoRNPs, involving, for instance, nucleocytoplasmic transport of snRNAs and intranuclear transport between compartments of snoRNAs. The phosphorylated adaptor for nuclear export (PHAX) is required for nuclear export of snRNAs in metazoans and also involved in the intranuclear transport of snoRNAs to Cajal bodies. PHAX contains a conserved single-stranded nucleic acid binding domain (RNA_GG_bind domain) with no sequence homology with any other known RNA-binding module. Here, we report NMR and X-ray crystallography studies that elucidate the structural basis for RNA recognition by the PHAX RNA-binding domain (PHAX-RBD). The crystal structure of the RNA_GG_bind domain from the parasite Cryptosporidium parvum (Cp RBD) forms well-folded dimers in solution in the absence of any ligand. The human PHAX-RBD is monomeric and only adopts a tertiary fold upon RNA binding. The PHAX-RBD represents a novel helical fold and binds single-stranded RNA with micromolar affinity without sequence specificity. RNA recognition by human PHAX-RBD is consistent with mutational analysis that affects RNA binding and PHAX-mediated nuclear export. Our data suggest that the PHAX-RBD mediates auxiliary RNA contacts with the snRNA and snoRNA substrates that are required for transport and/or substrate release.
Structure and RNA recognition by the snRNA and snoRNA transport factor PHAX.,Mourao A, Varrot A, Mackereth CD, Cusack S, Sattler M RNA. 2010 Jun;16(6):1205-16. Epub 2010 Apr 29. PMID:20430857[3]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Boulon S, Verheggen C, Jady BE, Girard C, Pescia C, Paul C, Ospina JK, Kiss T, Matera AG, Bordonne R, Bertrand E. PHAX and CRM1 are required sequentially to transport U3 snoRNA to nucleoli. Mol Cell. 2004 Dec 3;16(5):777-87. PMID:15574332 doi:10.1016/j.molcel.2004.11.013
- ↑ Watkins NJ, Lemm I, Ingelfinger D, Schneider C, Hossbach M, Urlaub H, Luhrmann R. Assembly and maturation of the U3 snoRNP in the nucleoplasm in a large dynamic multiprotein complex. Mol Cell. 2004 Dec 3;16(5):789-98. PMID:15574333 doi:http://dx.doi.org/10.1016/j.molcel.2004.11.012
- ↑ Mourao A, Varrot A, Mackereth CD, Cusack S, Sattler M. Structure and RNA recognition by the snRNA and snoRNA transport factor PHAX. RNA. 2010 Jun;16(6):1205-16. Epub 2010 Apr 29. PMID:20430857 doi:10.1261/rna.2009910
