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J. Cell Biol.,
Volume 142, Number 2, July 27, 1998 319-329
Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461
Coiled bodies are small nuclear organelles
that are highly enriched in small nuclear RNAs, and
that have long been thought to be associated with the
nucleolus. Here we use mutational analysis, transient
transfections, and the yeast two-hybrid system to show that the nucleolar phosphoprotein Nopp140 functions
as a molecular link between the two prominent nuclear
organelles. Exogenous Nopp140 accumulated in the nucleolus rapidly, but only after a lag phase in coiled bodies, suggesting a pathway between the two organelles. The expression of partial Nopp140 constructs exerted
dominant negative effects on the endogenous Nopp140
by chasing it and other antigens that were common to
both organelles out of the nucleolus. The alternating
positively and negatively charged repeat domain of
Nopp140 was required for targeting to both organelles. In
addition, partial Nopp140 constructs caused formation of
novel structures in the nucleoplasm and, in the case
of the conserved carboxy terminus, led to the dispersal of
coiled bodies. As a final link, we identified the coiled
body-specific protein p80 coilin in a yeast two-hybrid screen with Nopp140. The interaction of the two proteins was confirmed by coimmunoprecipitation. Taken
together, Nopp140 appeared to shuttle between the nucleolus and the coiled bodies, and to chaperone the
transport of other molecules.
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