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Vol. 17, Issue 1, 32-42, January 2006

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Chironomus tentans-Repressor Splicing Factor Represses SR Protein Function Locally on Pre-mRNA Exons and Is Displaced at Correct Splice Sites

Petra Björk, Ingela Wetterberg-Strandh ^*, Göran Baurén , and Lars Wieslander

Department of Molecular Biology and Functional Genomics, Stockholm University, SE-106 91 Stockholm, Sweden

Submitted April 22, 2005; Revised September 14, 2005; Accepted October 7, 2005
Monitoring Editor: Greg Matera

Chironomus tentans-repressor splicing factor (Ct-RSF) represses the activation of splicing by SR proteins in vitro. Ct-RSF colocalizes with the Ser-Arg-rich (SR) protein hrp45 in interchromatin granule clusters and coimmunoprecipitates with hrp45 in nuclear extracts. Ct-RSF and hrp45 can also interact directly in vitro. Ct-RSF and hrp45 are recruited together to transcribing genes and associate with growing pre-mRNAs. Ct-RSF and hrp45 colocalize at a large number of gene loci. Injection of anti-Ct-RSF antibodies into nuclei of living cells blocks association of both Ct-RSF and hrp45 with the growing pre-mRNA, whereas binding of U2 small nuclear ribonucleoprotein particle (snRNP) to the pre-mRNA is unaffected. On the intron-rich Balbiani ring (BR) 3 pre-mRNA, hrp45 as well as U1 and U2 snRNPs bind extensively, whereas relatively little Ct-RSF is present. In contrast, the BR1 and BR2 pre-mRNAs, dominated by exon sequences, bind relatively much Ct-RSF compared with hrp45 and snRNPs. Our data suggest that Ct-RSF represses SR protein function at exons and that the assembly of spliceosomes at authentic splice sites displaces Ct-RSF locally.

^* Present address: AstraZeneca R & D, SE-151 85 Södertälje, Sweden

Present address: Global Genomics, Tomtebodavägen 21, SE-171 77 Stockholm, Sweden.

Address correspondence to: Lars Wieslander (lars.wieslander{at}molbio.su.se).