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Mol. Cell. Biol., 10 1997, 5803-5812, Vol 17, No. 10
DA Dunbar, S Wormsley, TM Agentis and SJ Baserga
We have isolated and characterized Mpp10p, a novel protein component of the
U3 small nucleolar ribonucleoprotein (snoRNP) from the yeast Saccharomyces
cerevisiae. The MPP10 protein was first identified in human cells by its
reactivity with an antibody that recognizes specific sites of mitotic
phosphorylation. To study the functional role of MPP10 in pre-rRNA
processing, we identified the yeast protein by performing a GenBank search.
The yeast Mpp10p homolog is 30% identical to the human protein over its
length. Antibodies to the purified yeast protein recognize a 110-kDa
polypeptide in yeast extracts and immunoprecipitate the U3 snoRNA,
indicating that Mpp10p is a specific protein component of the U3 snoRNP in
yeast. As a first step in the genetic analysis of Mpp10p function, diploid
S. cerevisiae cells were transformed with a null allele. Sporulation and
tetrad analysis indicate that MPP10 is an essential gene. A strain was
constructed where Mpp10p is expressed from a galactose-inducible, glucose-
repressible promoter. After depletion of Mpp10p by growth in glucose, cell
growth is arrested and levels of 18S and its 20S precursor are reduced or
absent while the 23S and 35S precursors accumulate. This pattern of
accumulation of rRNA precursors suggests that Mpp10p is required for
cleavage at sites A0, A1, and A2. Pulse-chase analysis of newly synthesized
pre-rRNAs in Mpp10p-depleted yeast confirms that little mature 18S rRNA
formed. These results reveal a novel protein essential for ribosome
biogenesis and further elucidate the composition of the U3 snoRNP.
Copyright © 1997, American Society for Microbiology
Mpp10p, a U3 small nucleolar ribonucleoprotein component required for pre-18S rRNA processing in yeast
Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut 06520-8040, USA.
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