Published online 13 June 2006
© 2006 The Author(s)
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The nucleolar protein Esf2 interacts directly with the DExD/H box RNA helicase, Dbp8, to stimulate ATP hydrolysis
1 Departments of Molecular Biophysics and Biochemistry, Yale University School of Medicine New Haven, Connecticut 06520, USA 2 Genetics, Yale University School of Medicine New Haven, Connecticut 06520, USA 3 Therapeutic Radiology, Yale University School of Medicine New Haven, Connecticut 06520, USA
*To whom correspondence should be addressed at Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, 333 Cedar Street, SHM C-114, 06520-8024, USA. Tel: 203 785 4618; Fax: 203 785 6404; Email: susan.baserga{at}yale.edu
Received April 18, 2006. Revised May 2, 2006. Accepted May 19, 2006.
While 18 putative RNA helicases are involved in ribosome biogenesis in Saccharomyces cerevisiae, their enzymatic properties have remained largely biochemically uncharacterized. To better understand their function, we examined the enzymatic properties of Dpb8, a DExD/H box protein previously shown to be required for the synthesis of the 18S rRNA. As expected for an RNA helicase, we demonstrate that recombinant Dbp8 has ATPase activity in vitro, and that this activity is dependent on an intact ATPase domain. Strikingly, we identify Esf2, a nucleolar putative RNA binding protein, as a binding partner for Dbp8, and show that it enhances Dbp8 ATPase activity by decreasing the KM for ATP. Thus, we have uncovered Esf2 as the first example of a protein co-factor that has a stimulatory effect on a nucleolar RNA helicase. We show that Esf2 can bind to pre-rRNAs and speculate that it may function to bring Dbp8 to the pre-rRNA, thereby both regulating its enzymatic activity and guiding Dbp8 to its site of action.
The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors
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