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Molecular and Cellular Biology, May 2008, p. 3045-3057, Vol. 28, No. 9
0270-7306/08/$08.00+0     doi:10.1128/MCB.02015-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Splicing Factors SF1 and U2AF Associate in Extraspliceosomal Complexes{triangledown} ,{dagger}

José Rino,1,{ddagger} Joana M. P. Desterro,1,{ddagger} Teresa R. Pacheco,1 Theodorus W. J. Gadella Jr.,2 and Maria Carmo-Fonseca1*

Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, 1649-028 Lisbon, Portugal,1 Molecular Cytology Section, Swammerdam Institute for Life Sciences, University of Amsterdam, Kruislaan 316, 1098 SM Amsterdam, The Netherlands2

Received 8 November 2007/ Returned for modification 12 December 2007/ Accepted 12 February 2008

Splicing factors SF1 and U2AF associate cooperatively with pre-mRNA and play a crucial role in 3' splice site recognition during early steps of spliceosome assembly. Formation of the active spliceosome subsequently displaces SF1 in a remodeling process that stabilizes the association of U2 snRNP with pre-mRNA. Fluorescence microscopy shows SF1 and U2AF distributed throughout the nucleoplasm, where transcription occurs, with additional concentration in nuclear speckles, where splicing factors accumulate when not engaged in splicing. Fluorescence recovery after photobleaching analysis in live cells shows that the mobilities of SF1 and the two subunits of U2AF (U2AF65 and U2AF35) are correlated with the abilities of these proteins to interact with each other. Direct binding of SF1 to U2AF65 was demonstrated by fluorescence resonance energy transfer in both the nucleoplasm and nuclear speckles. This interaction persisted after transcription inhibition, suggesting that SF1 associates with U2AF in a splicing-independent manner. We propose that SF1 and U2AF form extraspliceosomal complexes before and after taking part in the assembly of catalytic spliceosomes.

* Corresponding author. Mailing address: Instituto de Medicina Molecular, Faculdade de Medicina, Av. Prof. Egas Moniz, 1649-028 Lisboa, Portugal. Phone: 351 21 7999411. Fax: 351 21 7999412. E-mail: carmo.fonseca{at}fm.ul.pt

{triangledown} Published ahead of print on 19 February 2008.

{dagger} Supplemental material for this article may be found at http://mcb.asm.org/.

{ddagger} J.R. and J.M.P.D. contributed equally to the work.

Molecular and Cellular Biology, May 2008, p. 3045-3057, Vol. 28, No. 9
0270-7306/08/$08.00+0     doi:10.1128/MCB.02015-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



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  • Ellis, J. D., Lleres, D., Denegri, M., Lamond, A. I., Caceres, J. F. (2008). Spatial mapping of splicing factor complexes involved in exon and intron definition. JCB 181: 921-934 [Abstract] [Full Text]  


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