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Molecular and Cellular Biology, September 2005, p. 7484-7493, Vol. 25, No. 17
0270-7306/05/$08.00+0     doi:10.1128/MCB.25.17.7484-7493.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

ATPase/Helicase Activities of p68 RNA Helicase Are Required for Pre-mRNA Splicing but Not for Assembly of the Spliceosome

Chunru Lin,^1, Liuqing Yang,^1, Jenny J. Yang,² Youliang Huang,³ and Zhi-Ren Liu^1*

Department of Biology,¹ Department of Chemistry, Georgia State University, Atlanta, Georgia 30303,² Department of Biology, Auburn University, Auburn, Alabama 36849³

Received 5 April 2005/ Returned for modification 27 April 2005/ Accepted 4 June 2005

We have previously demonstrated that p68 RNA helicase, as an essential human splicing factor, acts at the U1 snRNA and 5' splice site (5'ss) duplex in the pre-mRNA splicing process. To further analyze the function of p68 in the spliceosome, we generated two p68 mutants (motif V, RGLD to LGLD, and motif VI, HRIGR to HLIGR). ATPase and RNA unwinding assays demonstrated that the mutations abolished the RNA-dependent ATPase activity and RNA unwinding activity. The function of p68 in the spliceosome was abolished by the mutations, and the mutations also inhibited the dissociation of U1 from the 5'ss, while the mutants still interacted with the U1-5'ss duplex. Interestingly, the nonactive p68 mutants did not prevent the transition from prespliceosome to the spliceosome. The data suggested that p68 RNA helicase might actively unwind the U1-5'ss duplex. The protein might also play a role in the U4.U6/U5 addition, which did not require the ATPase and RNA unwinding activities of p68. In addition, we present evidence here to demonstrate the functional role of p68 RNA helicase in the pre-mRNA splicing process in vivo. Our experiments also showed that p68 interacted with unspliced but not spliced mRNA in vivo.

These authors contributed equally.

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