Functional separation of pre-rRNA processing steps revealed by truncation of the U3 small nucleolar ribonucleoprotein component, Mpp10

Yale University, New Haven, Connecticut, United States
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 01/1998; 94(25):13536-41. DOI: 10.1073/pnas.94.25.13536
Source: PubMed


The U3 small nucleolar ribonucleoprotein (snoRNP) is required for three cleavage events that generate the mature 18S rRNA from the pre-rRNA. In Saccharomyces cerevisiae, depletion of Mpp10, a U3 snoRNP-specific protein, halts 18S rRNA production and impairs cleavage at the three U3 snoRNP-dependent sites: A0, A1, and A2. We have identified truncation mutations of Mpp10 that affect 18S rRNA synthesis and confer cold-sensitivity and slow growth. However, distinct from yeast cells depleted of Mpp10, the mutants carrying these truncated Mpp10 proteins accumulate a novel precursor, resulting from cleavage at only A0. The Mpp10 truncations do not alter association of Mpp10 with the U3 snoRNA, nor do they affect snoRNA or protein stability. Thus, the role in processing of the U3 snoRNP can be separated into cleavage at the A0 site, which occurs in the presence of truncated Mpp10, and cleavage at the A1/A2 sites, which occurs only with intact Mpp10. These results strongly argue for a role for Mpp10 in processing at the A1/A2 sites.

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    • "The IMPQ strain appeared to be cold sensitive and its growth was lightly slowed compared to the wild-type strain. Both phenotypes were already reported for mutations affecting ribosome assembly, or pre-rRNA processing [11], notably with a Mpp10p mutant [7]. As expected, the IMPQ strain was impaired for ribosome biogenesis, presenting a decrease of free 40S ribosomal subunits and less mature 18S rRNA. "
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    ABSTRACT: In Saccharomyces cerevisiae, the essential IMP3 gene encodes a component of the SSU processome, a large ribonucleoprotein complex required for processing of small ribosomal subunit RNA precursors. Mutation of the IMP3 termination codon to a sense codon resulted in a viable mutant allele producing a C-terminal elongated form of the Imp3 protein. A strain expressing the mutant allele displayed ribosome biogenesis defects equivalent to IMP3 depletion. This hypomorphic allele represented a unique opportunity to investigate and better understand the Imp3p functions. We demonstrated that the +1 frameshifting was increased in the mutant strain. Further characterizations revealed involvement of the Imp3 protein in DNA repair and telomere length control, pointing to a functional relationship between both pathways and ribosome biogenesis.
    Full-text · Article · Apr 2011 · PLoS ONE
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    • "In mammalian cells, 18S rRNA processing is a highly complicated process in which many snoRNAs including box C/ D snoRNAs such as U3 and U14 and box H/ACA snoRNAs such as snR10 and snR30 are involved [29] [30]. Up to date, only a few nucleolar proteins such as MPP10 [31] [32] [33], Imp3p and Imp4p [34] [35] [36] [37], and hU3-55K [22] [38] [39] have been identified to be specifically associated with U3 snoRNA and the rest pre-rRNA processing proteins are associated with multiple snoRNPs. For example, mammalian protein 15.5K, which mediates U3 binding of hU3-55K, is involved in assembly of three RNP complexes, the U4/U6 snRNP, the box C/D snoRNP, and the U3 box B/C motifassociated RNP complex [40]. "
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    • "The SSU processome is required for pre-18S biogenesis at pre-rRNA processing sites A0, A1, and A2 (bold text). Oligos C, B, E, A, and Y were used as previously described (Lee and Baserga, 1997). Defects in these processing steps lead to accumulation of the 35S and 23S pre-rRNAs and a reduction in the 27SA2 and 20S pre-rRNAs and 18S rRNA. "
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