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Molecular and Cellular Biology, November 1998, p. 6756-6766, Vol. 18, No. 11
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

The Human U5-220kD Protein (hPrp8) Forms a Stable RNA-Free Complex with Several U5-Specific Proteins, Including an RNA Unwindase, a Homologue of Ribosomal Elongation Factor EF-2, and a Novel WD-40 Protein

Tilmann Achsel, Katharina Ahrens,dagger Hero Brahms, Stefan Teigelkamp,Dagger and Reinhard Lührmann*

Institut für Molekularbiologie und Tumorforschung, Philipps-Universität Marburg, 35037 Marburg, Germany

Received 4 May 1998/Returned for modification 16 June 1998/Accepted 12 August 1998

The human small nuclear ribonucleoprotein (snRNP) U5 is biochemically the most complex of the snRNP particles, containing not only the Sm core proteins but also 10 particle-specific proteins. Several of these proteins have sequence motifs which suggest that they participate in conformational changes of RNA and protein. Together, the specific proteins comprise 85% of the mass of the U5 snRNP particle. Therefore, protein-protein interactions should be highly important for both the architecture and the function of this particle. We investigated protein-protein interactions using both native and recombinant U5-specific proteins. Native U5 proteins were obtained by dissociation of U5 snRNP particles with the chaotropic salt sodium thiocyanate. A stable, RNA-free complex containing the 116-kDa EF-2 homologue (116kD), the 200kD RNA unwindase, the 220kD protein, which is the orthologue of the yeast Prp8p protein, and the U5-40kD protein was detected by sedimentation analysis of the dissociated proteins. By cDNA cloning, we show that the 40kD protein is a novel WD-40 repeat protein and is thus likely to mediate regulated protein-protein interactions. Additional biochemical analyses demonstrated that the 220kD protein binds simultaneously to the 40- and the 116kD proteins and probably also to the 200kD protein. Since the 220kD protein is also known to contact both the pre-mRNA and the U5 snRNA, it is in a position to relay the functional state of the spliceosome to the other proteins in the complex and thus modulate their activity.

* Corresponding author. Mailing address: Institut für Molekularbiologie und Tumorforschung, Philipps-Universität Marburg, Emil Mannkopff-Str. 2, 35037 Marburg, Germany. Phone: (49) 6421 286240. Fax: (49) 6421 287008. E-mail: luehrmann{at}imt.uni-marburg.de.

dagger Present address: Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3204.

Dagger Present address: ScheboTech GmbH, 35435 Wettenberg, Germany.

Molecular and Cellular Biology, November 1998, p. 6756-6766, Vol. 18, No. 11
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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