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Molecular and Cellular Biology, October 2006, p. 7437-7450, Vol. 26, No. 20
0270-7306/06/$08.00+0     doi:10.1128/MCB.00664-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

The Helicase Has1p Is Required for snoRNA Release from Pre-rRNA{triangledown}

Xue-hai Liang and Maurille J. Fournier*

Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003

Received 17 April 2006/ Returned for modification 2 June 2006/ Accepted 4 August 2006

Synthesis of rRNA in eukaryotes involves the action of a large population of snoRNA-protein complexes (snoRNPs), which create modified nucleotides and participate in cleavage of pre-rRNA. The snoRNPs mediate these functions through direct base pairing, in many cases through long complementary sequences. This feature suggests that RNA helicases may be involved in the binding and release of snoRNPs from pre-rRNA. In this study, we determined that the DEAD box helicase Has1p, a nucleolar protein required for the production of 18S rRNA, copurifies with the snR30/U17 processing snoRNP but is also present with other snoRNPs. Blocking Has1p expression causes a substantial increase in snoRNPs associated with 60S-90S preribosomal RNP complexes, including the U3 and U14 processing snoRNPs and several modifying snoRNPs examined. Cosedimentation persisted even after deproteinization. This effect was not observed with depletion of two nonhelicase proteins, Esf1p and Dim2p, that are also required for 18S rRNA production. Point mutations in ATPase and helicase motifs of Has1p block U14 release from pre-rRNA. Surprisingly, depletion of Has1p causes a reduction in the level of free U6 snRNP. The results indicate that the Has1p helicase is required for snoRNA release from pre-rRNA and production of the U6 snRNP.

* Corresponding author. Mailing address: Department of Biochemistry and Molecular Biology, Lederle Graduate Research Center, University of Massachusetts, Amherst, MA 01003. Phone: (413) 545-2732, ext. 0566. Fax: (413) 545-3291. E-mail: 4nier{at}biochem.umass.edu.

{triangledown} Published ahead of print on 14 August 2006.

Molecular and Cellular Biology, October 2006, p. 7437-7450, Vol. 26, No. 20
0270-7306/06/$08.00+0     doi:10.1128/MCB.00664-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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