The DExH/D protein NPH-II remodels RNA-protein complexes
independently of duplex unwinding
Margaret E. Fairman1, Wen Wang1, Patricia A. Maroney2, Paul Gollnick3,
Reinhard Lührman4, Timothy W. Nilsen2 & Eckhard Jankowsky1,2
1
Department of Biochemistry, 2Center for RNA Molecular Biology, School of Medicine,
Case Western Reserve University, Cleveland, OH; 3Department of Biological Sciences,
SUNY at Buffalo, Buffalo, NY; 4Department of Cellular Biochemistry, Max Planck
Institute for Biophysical Chemistry, Göttingen, Germany
Virtually all aspects of RNA metabolism require DExH/D proteins, a large family of
nucleic acid activated NTPases. DExH/D proteins catalyze conformational changes in
RNA protein complexes, but their exact mechanisms of action remain elusive. Because
many DExH/D proteins can actively unwind RNA duplexes in vitro, it is widely assumed
that their biological functions are tied to the unwinding of duplex structures. However,
substrate structures for almost all DExH/D proteins are unknown, and it is therefore
unclear whether duplex unwinding is necessary for these enzymes to perform their
biological functions. Moreover, recent biochemical and genetic data suggest the
possibility that DExH/D proteins may rearrange RNA protein complexes by a mechanism
that does not require unwinding of RNA duplexes. Here we show that the DExH/D
protein NPH-II can indeed remodel several RNA-protein complexes independently of
duplex unwinding. Rather, NPH-II catalyzes remodeling of RNA-protein complexes
through ATP-driven tracking on single stranded RNA. These results raise the possibility
that the functions of DExH/D protein function are not restricted to duplex unwinding but
are exerted upon a wide range of physiological substrates.