Mutations in nucleolar proteins lead to nucleolar accumulation of polyA+ RNA in Saccharomyces cerevisiae.
Synthesis of mRNA and rRNA occur in the chromatin-rich nucleoplasm and the nucleolus, respectively. Nevertheless, we here report that a Saccharomyces cerevisiae gene, MTR3, previously implicated in mRNA transport, codes for a novel essential 28-kDa nucleolar protein. Moreover, in mtr3-1 the accumulated polyA+ RNA actually colocalizes with nucleolar antigens, the nucleolus becomes somewhat disorganized, and rRNA synthesis and processing are inhibited. A strain with a ts conditional mutation in RNA polymerase I also shows nucleolar accumulation of polyA+ RNA, whereas strains with mutations in the nucleolar protein Nop1p do not. Thus, in several mutant backgrounds, when mRNA cannot be exported i concentrates in the nucleolus. mRNA may normally encounter nucleolar components before export and proteins such as Mtr3p may be critical for export of both mRNA and ribosomal subunits.
Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA.
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Kadowaki
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Schneiter
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Hitomi
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Tartakoff
D000595:Amino Acid Sequence; D001483:Base Sequence; D001692:Biological Transport; D002466:Cell Nucleolus / Q000378:metabolism*; D003001:Cloning, Molecular; D005092:Exonucleases; D063326:Exosome Multienzyme Ribonuclease Complex; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D012319:RNA Polymerase II / Q000378:metabolism; D012331:RNA, Fungal / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins
D005656:Fungal Proteins; D009687:Nuclear Proteins; D012331:RNA, Fungal; D012333:RNA, Messenger; D012335:RNA, Ribosomal; D029701:Saccharomyces cerevisiae Proteins; D012319:RNA Polymerase II; D005092:Exonucleases; D063326:Exosome Multienzyme Ribonuclease Complex; C097433:MTR3 protein, S cerevisiae