6qx9
Structure of a human fully-assembled precatalytic spliceosome (pre-B complex).
Structural highlights
Disease[PRPF3_HUMAN] Defects in PRPF3 are the cause of retinitis pigmentosa type 18 (RP18) [MIM:601414]. RP leads to degeneration of retinal photoreceptor cells. Patients typically have night vision blindness and loss of midperipheral visual field. As their condition progresses, they lose their far peripheral visual field and eventually central vision as well. RP18 inheritance is autosomal dominant.[1] [2] [3] [U520_HUMAN] Retinitis pigmentosa. Retinitis pigmentosa 33 (RP33) [MIM:610359]: A retinal dystrophy belonging to the group of pigmentary retinopathies. Retinitis pigmentosa is characterized by retinal pigment deposits visible on fundus examination and primary loss of rod photoreceptor cells followed by secondary loss of cone photoreceptors. Patients typically have night vision blindness and loss of midperipheral visual field. As their condition progresses, they lose their far peripheral visual field and eventually central vision as well. Note=The disease is caused by mutations affecting the gene represented in this entry.[4] [5] [6] [7] [8] [PRP31_HUMAN] Defects in PRPF31 are the cause of retinitis pigmentosa type 11 (RP11) [MIM:600138]. RP leads to degeneration of retinal photoreceptor cells. Patients typically have night vision blindness and loss of midperipheral visual field. As their condition progresses, they lose their far peripheral visual field and eventually central vision as well. RP11 inheritance is autosomal dominant.[9] [10] [11] [12] [13] [U5S1_HUMAN] Mandibulofacial dysostosis-microcephaly syndrome. The disease is caused by mutations affecting the gene represented in this entry. [PRP8_HUMAN] Defects in PRPF8 are the cause of retinitis pigmentosa type 13 (RP13) [MIM:600059]. RP leads to degeneration of retinal photoreceptor cells. Patients typically have night vision blindness and loss of midperipheral visual field. As their condition progresses, they lose their far peripheral visual field and eventually central vision as well. RP13 inheritance is autosomal dominant.[14] [15] [:][16] [17] [SF3B4_HUMAN] Defects in SF3B4 are the cause of acrofacial dysostosis type 1 (AFD1) [MIM:154400]. AFD1 is a form of acrofacial dysostosis, a group of disorders which are characterized by malformation of the craniofacial skeleton and the limbs. The major facial features of AFD1 include downslanted palpebral fissures, midface retrusion, and micrognathia, the latter of which often requires the placement of a tracheostomy in early childhood. Limb defects typically involve the anterior (radial) elements of the upper limbs and manifest as small or absent thumbs, triphalangeal thumbs, radial hyoplasia or aplasia, and radioulnar synostosis. Phocomelia of the upper limbs and, occasionally, lower-limb defects have also been reported.[18] Function[SF3B3_HUMAN] Subunit of the splicing factor SF3B required for 'A' complex assembly formed by the stable binding of U2 snRNP to the branchpoint sequence (BPS) in pre-mRNA. Sequence independent binding of SF3A/SF3B complex upstream of the branch site is essential, it may anchor U2 snRNP to the pre-mRNA. May also be involved in the assembly of the 'E' complex. Belongs also to the minor U12-dependent spliceosome, which is involved in the splicing of rare class of nuclear pre-mRNA intron. [SF3A2_HUMAN] Subunit of the splicing factor SF3A required for 'A' complex assembly formed by the stable binding of U2 snRNP to the branchpoint sequence (BPS) in pre-mRNA. Sequence independent binding of SF3A/SF3B complex upstream of the branch site is essential, it may anchor U2 snRNP to the pre-mRNA. May also be involved in the assembly of the 'E' complex. [RUXE_HUMAN] Appears to function in the U7 snRNP complex that is involved in histone 3'-end processing. Associated with snRNP U1, U2, U4/U6 and U5. [LSM7_HUMAN] Binds specifically to the 3'-terminal U-tract of U6 snRNA and is probably a component of the spliceosome. [NH2L1_HUMAN] Binds to the 5'-stem-loop of U4 snRNA and may play a role in the late stage of spliceosome assembly. The protein undergoes a conformational change upon RNA-binding.[19] [20] [SMD2_HUMAN] Required for pre-mRNA splicing. Required for snRNP biogenesis (By similarity). [PRPF3_HUMAN] Participates in pre-mRNA splicing. May play a role in the assembly of the U4/U5/U6 tri-snRNP complex. [SNRPA_HUMAN] Binds stem loop II of U1 snRNA. It is the first snRNP to interact with pre-mRNA. This interaction is required for the subsequent binding of U2 snRNP and the U4/U6/U5 tri-snRNP. In a snRNP-free form (SF-A) may be involved in coupled pre-mRNA splicing and polyadenylation process. Binds preferentially to the 5'-UGCAC-3' motif in vitro.[21] [RSMB_HUMAN] Appears to function in the U7 snRNP complex that is involved in histone 3'-end processing. Associated with snRNP U1, U2, U4/U6 and U5. May have a functional role in the pre-mRNA splicing or in snRNP structure. Binds to the downstream cleavage product (DCP) of histone pre-mRNA in a U7 snRNP dependent manner (By similarity). [SNUT1_HUMAN] Plays a role in mRNA splicing as a component of the U4/U6-U5 tri-snRNP, one of the building blocks of the spliceosome. May also bind to DNA.[22] [LSM4_HUMAN] Binds specifically to the 3'-terminal U-tract of U6 snRNA. [RU2B_HUMAN] Involved in pre-mRNA splicing. This protein is associated with snRNP U2. It binds stem loop IV of U2 snRNA only in presence of the U2A' protein. [LSM6_HUMAN] Component of LSm protein complexes, which are involved in RNA processing and may function in a chaperone-like manner, facilitating the efficient association of RNA processing factors with their substrates. Component of the cytoplasmic LSM1-LSM7 complex, which is thought to be involved in mRNA degradation by activating the decapping step in the 5'-to-3' mRNA decay pathway. Component of the nuclear LSM2-LSM8 complex, which is involved in splicing of nuclear mRNAs. LSM2-LSM8 associates with multiple snRNP complexes containing the U6 snRNA (U4/U6 di-snRNP, spliceosomal U4/U6.U5 tri-snRNP, and free U6 snRNP). It binds directly to the 3'-terminal U-tract of U6 snRNA and plays a role in the biogenesis and stability of the U6 snRNP and U4/U6 snRNP complexes. LSM2-LSM8 probably also is involved degradation of nuclear pre-mRNA by targeting them for decapping, and in processing of pre-tRNAs, pre-rRNAs and U3 snoRNA (By similarity). [U520_HUMAN] RNA helicase that plays an essential role in pre-mRNA splicing as component of the U5 snRNP and U4/U6-U5 tri-snRNP complexes. Involved in spliceosome assembly, activation and disassembly. Mediates changes in the dynamic network of RNA-RNA interactions in the spliceosome. Catalyzes the ATP-dependent unwinding of U4/U6 RNA duplices, an essential step in the assembly of a catalytically active spliceosome.[23] [24] [25] [26] [DDX23_HUMAN] Involved in pre-mRNA splicing and its phosphorylated form (by SRPK2) is required for spliceosomal B complex formation.[27] [PRP31_HUMAN] Involved in pre-mRNA splicing. Required for U4/U6.U5 tri-snRNP formation.[28] [LSM3_HUMAN] Binds specifically to the 3'-terminal U-tract of U6 snRNA. [LSM8_HUMAN] Binds specifically to the 3'-terminal U-tract of U6 snRNA and is probably a component of the spliceosome. [SMD1_HUMAN] May act as a charged protein scaffold to promote snRNP assembly or strengthen snRNP-snRNP interactions through nonspecific electrostatic contacts with RNA. [LSM5_HUMAN] Plays a role in U6 snRNP assembly and function. Binds to the 3' end of U6 snRNA, thereby facilitating formation of the spliceosomal U4/U6 duplex formation in vitro. [RU1C_HUMAN] Component of the U1 snRNP, which is essential for recognition of the pre-mRNA 5' splice-site and the subsequent assembly of the spliceosome. U1-C is directly involved in initial 5' splice-site recognition for both constitutive and regulated alternative splicing. The interaction with the 5' splice-site seems to precede base-pairing between the pre-mRNA and the U1 snRNA. Stimulates E complex formation by stabilizing the base pairing of the 5' end of the U1 snRNA and the 5' splice-site region.[29] [30] [31] [SF3B2_HUMAN] Subunit of the splicing factor SF3B required for 'A' complex assembly formed by the stable binding of U2 snRNP to the branchpoint sequence (BPS) in pre-mRNA. Sequence independent binding of SF3A/SF3B complex upstream of the branch site is essential, it may anchor U2 snRNP to the pre-mRNA. May also be involved in the assembly of the 'E' complex. Belongs also to the minor U12-dependent spliceosome, which is involved in the splicing of rare class of nuclear pre-mRNA intron. [RU2A_HUMAN] This protein is associated with sn-RNP U2. It helps the A' protein to bind stem loop IV of U2 snRNA. [RUXF_HUMAN] Appears to function in the U7 snRNP complex that is involved in histone 3'-end processing. Associated with snRNP U1, U2, U4/U6 and U5. [U5S1_HUMAN] Component of the U5 snRNP and the U4/U6-U5 tri-snRNP complex required for pre-mRNA splicing. Binds GTP. [PRP4_HUMAN] Involved in pre-mRNA splicing. [SF3B1_HUMAN] Subunit of the splicing factor SF3B required for 'A' complex assembly formed by the stable binding of U2 snRNP to the branchpoint sequence (BPS) in pre-mRNA. Sequence independent binding of SF3A/SF3B complex upstream of the branch site is essential, it may anchor U2 snRNP to the pre-mRNA. May also be involved in the assembly of the 'E' complex. Belongs also to the minor U12-dependent spliceosome, which is involved in the splicing of rare class of nuclear pre-mRNA intron. [TXN4A_HUMAN] Essential role in pre-mRNA splicing. [PRP8_HUMAN] Central component of the spliceosome, which may play a role in aligning the pre-mRNA 5'- and 3'-exons for ligation. Interacts with U5 snRNA, and with pre-mRNA 5'-splice sites in B spliceosomes and 3'-splice sites in C spliceosomes. [SNR40_HUMAN] Component of the U5 small nuclear ribonucleoprotein (snRNP) complex. The U5 snRNP is part of the spliceosome, a multiprotein complex that catalyzes the removal of introns from pre-messenger RNAs.[32] [RU17_HUMAN] Mediates the splicing of pre-mRNA by binding to the loop I region of U1-snRNA. The truncated isoforms cannot bind U1-snRNA. [PHF5A_HUMAN] Acts as a transcriptional regulator by binding to the GJA1/Cx43 promoter and enhancing its up-regulation by ESR1/ER-alpha. Also involved in pre-mRNA splicing.[33] [RBM42_HUMAN] Binds (via the RRM domain) to the 3'-untranslated region (UTR) of CDKN1A mRNA. [SF3A1_HUMAN] Subunit of the splicing factor SF3A required for 'A' complex assembly formed by the stable binding of U2 snRNP to the branchpoint sequence (BPS) in pre-mRNA. Sequence independent binding of SF3A/SF3B complex upstream of the branch site is essential, it may anchor U2 snRNP to the pre-mRNA. May also be involved in the assembly of the 'E' complex. [SNR27_HUMAN] May play a role in mRNA splicing. [SNUT2_HUMAN] Plays a role in pre-mRNA splicing as a component of the U4/U6-U5 tri-snRNP, one of the building blocks of the spliceosome. Regulates AURKB mRNA levels, and thereby plays a role in cytokinesis and in the spindle checkpoint. Does not have ubiquitin-specific peptidase activity, but could be a competitor of ubiquitin C-terminal hydrolases (UCHs).[34] [35] [SF3B4_HUMAN] Subunit of the splicing factor SF3B required for 'A' complex assembly formed by the stable binding of U2 snRNP to the branchpoint sequence (BPS) in pre-mRNA. Sequence independent binding of SF3A/SF3B complex upstream of the branch site is essential, it may anchor U2 snRNP to the pre-mRNA. May also be involved in the assembly of the 'E' complex. SF3B4 has been found in complex 'B' and 'C' as well. Belongs also to the minor U12-dependent spliceosome, which is involved in the splicing of rare class of nuclear pre-mRNA intron. [RUXG_HUMAN] Appears to function in the U7 snRNP complex that is involved in histone 3'-end processing. Associated with snRNP U1, U2, U4/U6 and U5. [SF3A3_HUMAN] Subunit of the splicing factor SF3A required for 'A' complex assembly formed by the stable binding of U2 snRNP to the branchpoint sequence (BPS) in pre-mRNA. Sequence independent binding of SF3A/SF3B complex upstream of the branch site is essential, it may anchor U2 snRNP to the pre-mRNA. May also be involved in the assembly of the 'E' complex. [PRP4B_HUMAN] Has a role in pre-mRNA splicing. Phosphorylates SF2/ASF. [LSM2_HUMAN] Binds specifically to the 3'-terminal U-tract of U6 snRNA. May be involved in pre-mRNA splicing. [SMD3_HUMAN] Appears to function in the U7 snRNP complex that is involved in histone 3'-end processing. Binds to the downstream cleavage product (DCP) of histone pre-mRNA in a U7 snRNP dependent manner.[36] Publication Abstract from PubMedThe prespliceosome, comprising U1 and U2 snRNPs bound to the pre-mRNA 5' splice site (5'SS) and branch point sequence, associates with the U4/U6.U5 tri-snRNP to form the fully-assembled precatalytic pre-B spliceosome. Here, we report cryo-EM structures of the human pre-B complex captured before U1 snRNP dissociation at 3.3 A core resolution, and the human tri-snRNP at 2.9 A resolution. U1 snRNP inserts the 5'SS-U1 snRNA helix between the two RecA domains of the Prp28 DEAD-box helicase. ATP-dependent closure of the Prp28 RecA domains releases the 5'SS to pair with the nearby U6 ACAGAGA-box sequence presented as a mobile loop. The structures suggest that formation of the 5'SS-ACAGAGA helix triggers remodeling of an intricate protein-RNA network to induce Brr2 helicase relocation to its loading sequence in U4 snRNA, enabling Brr2 to unwind the U4/U6 snRNA duplex to allow U6 snRNA to form the catalytic center of the spliceosome. Mechanism of 5' splice site transfer for human spliceosome activation.,Charenton C, Wilkinson ME, Nagai K Science. 2019 Apr 11. pii: science.aax3289. doi: 10.1126/science.aax3289. PMID:30975767[37] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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