Human Molecular Genetics Advance Access published online on September 13, 2005
Human Molecular Genetics, doi:10.1093/hmg/ddi343
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1 Department of Biochemistry, Theodor Boveri Institute, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
* To whom correspondence should be addressed. Spliceosomal U snRNP assembly is an active process mediated by the macromolecular SMN-complex. This complex contains the survival motor neuron (SMN) protein and six additional proteins named Gemin2-7, according to their localization to nuclear structures termed gems. Here we provide biochemical evidence for the existence of another, yet atypical SMN-complex component, termed unrip. This abundant factor has previously been shown to form a complex with unr, a protein implicated in cap-independent translation of cellular and viral mRNA. We show that unrip is integrated into a complex with unr or with the SMN-complex in vivo in a mutually exclusive manner. In the latter case unrip is recruited to the active SMN-complex via a stable interaction with Gemin7. However, unlike SMN and Gemins, unrip localizes predominantly to the cytoplasm and is absent from gems/Cajal bodies. Interestingly, RNAi-induced reduction of unrip protein levels leads to enhanced accumulation of SMN in the nucleus as evident by the increased formation of nuclear gems/Cajal bodies. Our data identify unrip as the first component of the U snRNP assembly machinery that associates with the SMN-complex in a compartment-specific way. We speculate that unrip plays a crucial role in the intracellular distribution of the SMN-complex.
Received June 21, 2005
Revised August 31, 2005
Accepted September 7, 2005
Article
Unrip, a factor implicated in cap-independent translation, associates with the cytosolic SMN-complex and influences its intracellular localization
Utz Fischer, E-mail: utz.fischer{at}biozentrum.uni-wuerzburg.de
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