Human SAP18 mediates assembly of a splicing regulatory multiprotein complex via its ubiquitin-like fold.
RNPS1, Acinus, and SAP18 form the apoptosis- and splicing-associated protein (ASAP) complex, which is also part of the exon junction complex. Whereas RNPS1 was originally identified as a general activator of mRNA processing, all three proteins have been found within functional spliceosomes. Both RNPS1 and Acinus contain typical motifs of splicing regulatory proteins including arginine/serine-rich domains. Due to the absence of such structural features, however, a function of SAP18 in splicing regulation is completely unknown. Here we have investigated splicing regulatory activities of the ASAP components. Whereas a full-length Acinus isoform displayed only limited splicing regulatory activity, both RNPS1 and, surprisingly, SAP18 strongly modulated splicing regulation. Detailed mutational analysis and three-dimensional modeling data revealed that the ubiquitin-like fold of SAP18 was required for efficient splicing regulatory activity. Coimmunoprecipitation and immunofluorescence experiments demonstrated that SAP18 assembles a nuclear speckle-localized splicing regulatory multiprotein complex including RNPS1 and Acinus via its ubiquitin-like fold. Our results therefore suggest a novel function of SAP18 in splicing regulation.
Institute of Molecular Medicine, University of Düsseldorf, D-40225 Düsseldorf, Germany.
Kusum K
KK
Singh
Steffen
S
Erkelenz
Stephanie
S
Rattay
Anna Katharina
AK
Dehof
Andreas
A
Hildebrandt
Klaus
K
Schulze-Osthoff
Heiner
H
Schaal
Christian
C
Schwerk
D001483:Base Sequence; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D056970:Co-Repressor Proteins; D006367:HeLa Cells; D006801:Humans; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism*; D017510:Protein Folding; D055503:Protein Multimerization / Q000502:physiology; D017434:Protein Structure, Tertiary; D012326:RNA Splicing / Q000502:physiology; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins / Q000378:metabolism / Q000502:physiology; D017381:Spliceosomes / Q000378:metabolism*; D040681:Structural Homology, Protein; D025801:Ubiquitin / Q000737:chemistry*
D002352:Carrier Proteins; D056970:Co-Repressor Proteins; D046912:Multiprotein Complexes; D016601:RNA-Binding Proteins; C084538:RNPS1 protein, human; D012261:Ribonucleoproteins; C498650:SAP18 protein, human; D025801:Ubiquitin