The term non-coding is commonly employed for RNA that does not encode a protein, but this does not mean that such RNAs do not contain information nor have function. There is considerable evidence that the majority of mammalian and other complex organism's genomes is transcribed into non-coding RNAs, many of which are alternatively spliced and/or processed into smaller products. Around 98% of all transcriptional output in humans is non-coding RNA. RNA-mediated gene regulation is widespread in higher eukaryotes and complex genetic phenomena like RNA interference are mediated by such RNAs. These non-coding RNAs are a growing list and include rRNAs, tRNAs, snRNAs, snoRNAs siRNAs, 7SL RNA, 7SK RNA, the RNA component of RNase P RNA, the RNA component of RNase MRP, and the RNA component of telomerase.
Pellizzoni L, Kataoka N, Charroux B, Dreyfuss G.; ''A novel function for SMN, the spinal muscular atrophy disease gene product, in pre-mRNA splicing.''; PubMedEurope PMCScholia
Rabut G, Doye V, Ellenberg J.; ''Mapping the dynamic organization of the nuclear pore complex inside single living cells.''; PubMedEurope PMCScholia
Kabachinski G, Schwartz TU.; ''The nuclear pore complex--structure and function at a glance.''; PubMedEurope PMCScholia
Cronshaw JM, Krutchinsky AN, Zhang W, Chait BT, Matunis MJ.; ''Proteomic analysis of the mammalian nuclear pore complex.''; PubMedEurope PMCScholia
Carissimi C, Saieva L, Gabanella F, Pellizzoni L.; ''Gemin8 is required for the architecture and function of the survival motor neuron complex.''; PubMedEurope PMCScholia
Sleeman JE, Lamond AI.; ''Newly assembled snRNPs associate with coiled bodies before speckles, suggesting a nuclear snRNP maturation pathway.''; PubMedEurope PMCScholia
Kosinski J, Mosalaganti S, von Appen A, Teimer R, DiGuilio AL, Wan W, Bui KH, Hagen WJ, Briggs JA, Glavy JS, Hurt E, Beck M.; ''Molecular architecture of the inner ring scaffold of the human nuclear pore complex.''; PubMedEurope PMCScholia
Fontoura BM, Blobel G, Matunis MJ.; ''A conserved biogenesis pathway for nucleoporins: proteolytic processing of a 186-kilodalton precursor generates Nup98 and the novel nucleoporin, Nup96.''; PubMedEurope PMCScholia
Pellizzoni L, Baccon J, Rappsilber J, Mann M, Dreyfuss G.; ''Purification of native survival of motor neurons complexes and identification of Gemin6 as a novel component.''; PubMedEurope PMCScholia
Brahms H, Meheus L, de Brabandere V, Fischer U, Lührmann R.; ''Symmetrical dimethylation of arginine residues in spliceosomal Sm protein B/B' and the Sm-like protein LSm4, and their interaction with the SMN protein.''; PubMedEurope PMCScholia
Ori A, Banterle N, Iskar M, Iskar M, Andrés-Pons A, Escher C, Khanh Bui H, Sparks L, Solis-Mezarino V, Rinner O, Bork P, Lemke EA, Beck M.; ''Cell type-specific nuclear pores: a case in point for context-dependent stoichiometry of molecular machines.''; PubMedEurope PMCScholia
Plessel G, Fischer U, Lührmann R.; ''m3G cap hypermethylation of U1 small nuclear ribonucleoprotein (snRNP) in vitro: evidence that the U1 small nuclear RNA-(guanosine-N2)-methyltransferase is a non-snRNP cytoplasmic protein that requires a binding site on the Sm core domain.''; PubMedEurope PMCScholia
Segref A, Mattaj IW, Ohno M.; ''The evolutionarily conserved region of the U snRNA export mediator PHAX is a novel RNA-binding domain that is essential for U snRNA export.''; PubMedEurope PMCScholia
Neuenkirchen N, Englbrecht C, Ohmer J, Ziegenhals T, Chari A, Fischer U.; ''Reconstitution of the human U snRNP assembly machinery reveals stepwise Sm protein organization.''; PubMedEurope PMCScholia
Lin DH, Stuwe T, Schilbach S, Rundlet EJ, Perriches T, Mobbs G, Fan Y, Thierbach K, Huber FM, Collins LN, Davenport AM, Jeon YE, Hoelz A.; ''Architecture of the symmetric core of the nuclear pore.''; PubMedEurope PMCScholia
Charroux B, Pellizzoni L, Perkinson RA, Shevchenko A, Mann M, Dreyfuss G.; ''Gemin3: A novel DEAD box protein that interacts with SMN, the spinal muscular atrophy gene product, and is a component of gems.''; PubMedEurope PMCScholia
Suntharalingam M, Wente SR.; ''Peering through the pore: nuclear pore complex structure, assembly, and function.''; PubMedEurope PMCScholia
Mouaikel J, Narayanan U, Verheggen C, Matera AG, Bertrand E, Tazi J, Bordonné R.; ''Interaction between the small-nuclear-RNA cap hypermethylase and the spinal muscular atrophy protein, survival of motor neuron.''; PubMedEurope PMCScholia
Narayanan U, Ospina JK, Frey MR, Hebert MD, Matera AG.; ''SMN, the spinal muscular atrophy protein, forms a pre-import snRNP complex with snurportin1 and importin beta.''; PubMedEurope PMCScholia
Baccon J, Pellizzoni L, Rappsilber J, Mann M, Dreyfuss G.; ''Identification and characterization of Gemin7, a novel component of the survival of motor neuron complex.''; PubMedEurope PMCScholia
Charroux B, Pellizzoni L, Perkinson RA, Yong J, Shevchenko A, Mann M, Dreyfuss G.; ''Gemin4. A novel component of the SMN complex that is found in both gems and nucleoli.''; PubMedEurope PMCScholia
Friesen WJ, Dreyfuss G.; ''Specific sequences of the Sm and Sm-like (Lsm) proteins mediate their interaction with the spinal muscular atrophy disease gene product (SMN).''; PubMedEurope PMCScholia
Meister G, Eggert C, Fischer U.; ''SMN-mediated assembly of RNPs: a complex story.''; PubMedEurope PMCScholia
Gubitz AK, Mourelatos Z, Abel L, Rappsilber J, Mann M, Dreyfuss G.; ''Gemin5, a novel WD repeat protein component of the SMN complex that binds Sm proteins.''; PubMedEurope PMCScholia
Bühler D, Raker V, Lührmann R, Fischer U.; ''Essential role for the tudor domain of SMN in spliceosomal U snRNP assembly: implications for spinal muscular atrophy.''; PubMedEurope PMCScholia
The snRNA:SMN:SM protein complex is engaged by a hypermethylase that hypermethylates the snRNA cap from
m7G (7-methylguanosine) to m3G (2,2,7-trimethylguanosine).
A properly assembled Sm core and the m3G cap structure are prerequisites for small nuclear ribonucleoprotein (snRNP) import into the nucleus. Once imported into the nucleus, the snRNPs are initially concentrated in Cajal bodies (CBs), where there is further processing of the snRNAs plus binding of additional proteins, from CRBs they transit to "speckles", from where they are engaged for pre-mRNA splicing. The SMN complexes in the nucleus are found throughout the nucleoplasm but are particularly concentrated in Gems, the "twins" of the snRNP-rich CBs.
The survival of motor neurons (SMN) complex binds to Sm proteins and small nuclear RNAs (snRNAs) in the cytoplasm. Sm is part the SMN multiprotein complex that contains Gemins 2 – 7, including the DEAD-box RNA helicase Gemin3. The binding of the SMN complex to the snRNAs depends on the presence of specific, high-affinity (nanomolar) binding domains in the snRNAs. The SMN complex binds the Sm proteins through the Sm domains interaction with the Gemins, the TUDOR domain, and through unique arginine- and glycine-rich (RG) domains found in three of these, SmB, SmD1 and SmD3. The association with RG domains is strongly enhanced by the post-translational symmetric dimethylation of specific arginines in these domains, a process that is carried out by the methylosome (JBP1 or PRMT5) complex.
The snRNAs, except U6 snRNA, are transcribed by RNA polymerase II, co-transcriptionally capped and exported rapidly to the cytoplasm in association with a cap-binding complex and the export factor PHAX.
The nuclear import signal has two parts; Cap hypermethylation triggers nuclear import via snurportin1 binding and by receptor recognition of the Sm proteins. Snurportin1 (SPN) is an adaptor that links the assembled snRNP to the nuclear transport machinery, recruiting importin beta for nuclear import. The import receptor that recognizes the Sm proteins is not yet known.
To facilitate snRNP assembly, the SMN complex must bring together the Sm proteins and an Sm-site-containing snRNA. The SMN:Sm protein complex binds to the m7G capped snRNAs in the cytoplasm.
Original Pathway at Reactome: http://www.reactome.org/PathwayBrowser/#DB=gk_current&FOCUS_SPECIES_ID=48887&FOCUS_PATHWAY_ID=194441
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SMN SM
Snurportin complexCBC
PHAX complexAnnotated Interactions