PathwayStep438 PathwayStep439 PathwayStep436 PathwayStep437 PathwayStep435 PathwayStep440 Loading and methylation of Sm proteins onto SMN Complexes snRNP complex assembly Nuclear export of snRNA transcripts snRNP nuclear import and release snRNA Cap hypermethylation snRNP:Snurportin complex formation snRNP Assembly Authored: Gillespie, ME, 2007-01-29 20:29:54 GENE ONTOLOGYGO:0000387 Pubmed15130578 Reactome Database ID Release 43191859 Reactome, http://www.reactome.org ReactomeREACT_11066 Reviewed: Luhrmann, R, 2007-04-30 18:31:22 Small nuclear ribonucleoproteins (snRNPs) are crucial for pre-mRNA processing to mRNAs. Each snRNP contains a small nuclear RNA (snRNA) and an extremely stable core of seven Sm proteins. The U6 snRNA differs from the other snRNAs; it binds seven Sm-like proteins and its assembly does not involve a cytoplasmic phase. The snRNP biogenesis pathway for all of the other snRNAs is complex, involving nuclear export of snRNA, Sm-core assembly in the cytoplasm and re-import of the mature snRNP. The assembly of the snRNA:Sm-core is carried out by the survival of motor neurons (SMN) complex. The SMN complex stringently scrutinizes RNAs for specific features that define them as snRNAs and binds the RNA-binding Sm proteins.