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Molecular and Cellular Biology, October 2007, p. 6782-6793, Vol. 27, No. 19
0270-7306/07/$08.00+0 doi:10.1128/MCB.01097-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

ICaMB, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, United Kingdom,1 IGMM, CNRS UMR5535, Montpellier, France2
Received 20 June 2007/ Accepted 6 July 2007
The box C/D small nucleolar RNPs (snoRNPs) are essential for the processing and modification of rRNA. The core box C/D proteins are restructured during human U3 box C/D snoRNP biogenesis; however, the molecular basis of this is unclear. Here we show that the U8 snoRNP is also restructured, suggesting that this may occur with all box C/D snoRNPs. We have characterized four novel human biogenesis factors (BCD1, NOP17, NUFIP, and TAF9) which, along with the ATPases TIP48 and TIP49, are likely to be involved in the formation of the pre-snoRNP. We have analyzed the in vitro protein-protein interactions between the assembly factors and core box C/D proteins. Surprisingly, this revealed few interactions between the individual core box C/D proteins. However, the novel biogenesis factors and TIP48 and TIP49 interacted with one or more of the core box C/D proteins, implying that they mediate the assembly of the pre-snoRNP. Consistent with this, we show that NUFIP bridges interactions between the core box C/D proteins in a partially reconstituted pre-snoRNP. Restructuring of the core complex probably reflects the conversion of the pre-snoRNP, where core protein-protein interactions are maintained by the bridging biogenesis factors, to the mature snoRNP.
Published ahead of print on 16 July 2007.
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