Preferred Label : Spliceosome Assembly Pathway;
NCIt related terms : Spliceosome Assembly;
Alternative definition : BIOCARTA: The assembly of the spliceosome is a dynamic process that involves both
small ribonucleoprotein particles (snRNPs), and non-snRNP proteins. The complete spliceosome
consists of 5 snRNPs (U1, U2, U4, U5, and U6) and 50-100 non-snRNP factors. The snRNPs
themselves contain a snRNA and a number of different proteins. These proteins can
be subdivided into two classes, those specific to the individual snRNP, and those
common to all snRNPs. The later group consists of eight polypeptides; B, B', D1, D2,
D3, E, F, and G, which bind together in a tight association, and are referred to as
the sm proteins. While some of the particle-specific proteins have been well studied,
i.e.U1-70K or U1-A, many have only been identified by their molecular weight and have
yet to be cloned. These snRNP components are recruited to the pre-mRNA in an ordered
manner, and begin with the recognition of exon-intron boundaries. The 5' end of the
U1 snRNP recognizes the 5' splice site of the pre-mRNA. This interaction is mediated
through conventional base pairing. Subsequently snRNP U1 recognizes and binds to the
conserved branch point adenosine site. This step in the splicing cycle is called the
commitment complex (CC) and is defined as a point where the formation of a stable
splicing complex commits the spliceosome to assemble. Binding of the U1 snRNP encourages
binding of U2 snRNP, and is helped by U2AF protein. SR proteins such as ASF/SF2 and
SC35, or other intron bridging proteins, mediate the interaction between U1, U2 and
U2AF. Binding of these factors facilitate recognition of the 3' splice site, and this
whole complex is called the E (Early) complex. Spliceosomal A Complex is formed following
recruitment of U2 snRNP to the branch point sequence. Meanwhile, snRNPs U4/U6 and
U5 have formed a functional tri-snRNP complex. The association of the tri-snRNP U4/U6-U5
with the pre-spliceosome creates the B complex. Several RNA:RNA interactions occur
following this point, including the disassociation of the U4/U6 snRNP and the pairing
of the 3' end of U6 with the 5' end of U2. These, and other, complex RNA rearrangements
are required for mature spliceosomal formation, which is a pre requisite for the transesterification
reactions that create the spliced mRNA. (This definition may be outdated - see the
DesignNote.);
NCIt note : The BIOCARTA Definition (ALT_DEFINITION) for this pathway concept was provided by
BioCarta. This property was not created by, nor is it maintained by the NCI Thesaurus
staff. Additionally, BioCarta is no longer updating its pathway data; thus, the BIOCARTA
Definition might be outdated or inaccurate. Please see the Terms and Conditions for
Use at http://www.biocarta.com/.;
NCI Metathesaurus CUI : CL019091;
Biocarta ID : h_smPathway;
Origin ID : C39233;
UMLS CUI : C1158740;
Automatic exact mappings (from CISMeF team)
Semantic type(s)
has_gene_product_element
pathway_has_gene_element