Human SAP18 mediates assembly of a splicing regulatory multiprotein complex via its ubiquitin-like fold

Abstract

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.

Citation

[SER+10] Singh, K.K., Erkelenz, S., Rattay, S., Dehof, A.-K., Hildebrandt, A., Schulze-Osthoff, K., Schaal, H., and Schwerk, C.: Human SAP18 mediates assembly of a splicing regulatory multiprotein complex via its ubiquitin-like fold. RNA, 2010, 16(12), 2442-2454, 2010.
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