title: Components of an interdependent unit within the SSU processome regulate and mediate its activity.
abstract: The SSU processome is required for production of the small ribosomal subunit RNA, the 18S rRNA. Specifically, the U3 small nucleolar RNA (snoRNA) component of the SSU processome is essential for the formation of the conserved central pseudoknot and for cleavages of the pre-rRNA, both of which are required for 18S maturation. To further elucidate how these events are mediated, we examined the regulatory and mechanistic roles of the U3 specific proteins: Imp3p, Imp4p, and Mpp10p. We found that these proteins demonstrated an interdependence with respect to their stability and to their association with the U3 snoRNA. Because mutations in the U3 snoRNA that disrupt pre-rRNA processing confer similar defects on growth and pre-rRNA processing as do carboxy-terminal truncations of Mpp10p, we hypothesized that Mpp10p may be involved in maintaining U3 snoRNA-pre-rRNA base pairing. However, combining the two mutations resulted in a more pronounced cleavage defect at site A(2), suggesting that Mpp10p is also required at an additional mechanistic step. Furthermore, heterologous complementation experiments demonstrate that the last 95 amino acids of yeast Mpp10p are specifically required for growth and pre-rRNA processing at low temperatures.
authors.affiliation: Departments of Genetics. Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut 06520-8040, USA.
authors.forename: Karen A
authors.initials: KA
authors.lastname: Wehner
authors.forename: Jennifer E G
authors.initials: JE
authors.lastname: Gallagher
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Baserga
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D012322:RNA Precursors / Q000737:chemistry / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D012331:RNA, Fungal / Q000737:chemistry / Q000378:metabolism*; D012337:RNA, Ribosomal, 18S / Q000737:chemistry / Q000378:metabolism*; D020537:RNA, Small Nucleolar / Q000737:chemistry / Q000378:metabolism*; D012261:Ribonucleoproteins / Q000235:genetics / Q000378:metabolism*; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid
chemical_list: D005656:Fungal Proteins; C120533:IMP3 protein, S cerevisiae; C120534:IMP4 protein, S cerevisiae; C111098:MPP10 protein, S cerevisiae; D010750:Phosphoproteins; D012322:RNA Precursors; D012331:RNA, Fungal; D012337:RNA, Ribosomal, 18S; D020537:RNA, Small Nucleolar; C117378:RNA, U3 small nucleolar; D012261:Ribonucleoproteins; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins