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Molecular and Cellular Biology, September 2009, p. 4971-4981, Vol. 29, No. 18
0270-7306/09/$08.00+0     doi:10.1128/MCB.00752-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Evidence that the AAA+ Proteins TIP48 and TIP49 Bridge Interactions between 15.5K and the Related NOP56 and NOP58 Proteins during Box C/D snoRNP Biogenesis{triangledown}

Kenneth Scott McKeegan, Charles Maurice Debieux, and Nicholas James Watkins*

RNA Biology Group, ICaMB, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, United Kingdom

Received 10 June 2009/ Returned for modification 2 July 2009/ Accepted 10 July 2009

The box C/D small nucleolar RNPs (snoRNPs) are essential for the processing and modification of rRNA. TIP48 and TIP49 are two related AAA+ proteins that are essential for the formation of box C/D snoRNPs. These proteins are key components of the pre-snoRNP complexes, but their exact role in box C/D snoRNP biogenesis is largely uncharacterized. Here we report that TIP48 and TIP49 interact with one another in vitro, and only the TIP48/TIP49 complex, but not the individual proteins, possesses significant ATPase activity. Loss of TIP48 and TIP49 results in a change in pre-snoRNA levels and a loss of U3 snoRNA signal in the Cajal body. We show that TIP48 and TIP49 make multiple interactions with core snoRNP proteins and biogenesis factors and that these interactions are often regulated by the presence of ATP. Furthermore, we demonstrate that TIP48 and TIP49 efficiently bridge interactions between the core box C/D proteins NOP56 or NOP58 and 15.5K. Our data imply that the snoRNP assembly factor NUFIP can regulate the interactions between TIP48 and TIP49 and the core box C/D proteins. We suggest that snoRNP assembly involves an intricate series of interactions that are mediated/regulated by bridging factors and chaperones.

* Corresponding author. Mailing address: Institute for Cell and Molecular Biosciences, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, United Kingdom. Phone: 44 191 222 6991. Fax: 44 191 222 7424. E-mail: n.j.watkins{at}ncl.ac.uk

{triangledown} Published ahead of print on 20 July 2009.

Molecular and Cellular Biology, September 2009, p. 4971-4981, Vol. 29, No. 18
0270-7306/09/$08.00+0     doi:10.1128/MCB.00752-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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