title: Bud23 methylates G1575 of 18S rRNA and is required for efficient nuclear export of pre-40S subunits.
abstract: BUD23 was identified from a bioinformatics analysis of Saccharomyces cerevisiae genes involved in ribosome biogenesis. Deletion of BUD23 leads to severely impaired growth, reduced levels of the small (40S) ribosomal subunit, and a block in processing 20S rRNA to 18S rRNA, a late step in 40S maturation. Bud23 belongs to the S-adenosylmethionine-dependent Rossmann-fold methyltransferase superfamily and is related to small-molecule methyltransferases. Nevertheless, we considered that Bud23 methylates rRNA. Methylation of G1575 is the only mapped modification for which the methylase has not been assigned. Here, we show that this modification is lost in bud23 mutants. The nuclear accumulation of the small-subunit reporters Rps2-green fluorescent protein (GFP) and Rps3-GFP, as well as the rRNA processing intermediate, the 5' internal transcribed spacer 1, indicate that bud23 mutants are defective for small-subunit export. Mutations in Bud23 that inactivated its methyltransferase activity complemented a bud23Delta mutant. In addition, mutant ribosomes in which G1575 was changed to adenosine supported growth comparable to that of cells with wild-type ribosomes. Thus, Bud23 protein, but not its methyltransferase activity, is important for biogenesis and export of the 40S subunit in yeast.
authors.affiliation: Section of Molecular Genetics and Microbiology, 1 University Station, A5000, The University of Texas at Austin, Austin, TX 78712-0162, USA.
authors.forename: Joshua
authors.initials: J
authors.lastname: White
authors.forename: Zhihua
authors.initials: Z
authors.lastname: Li
authors.forename: Richa
authors.initials: R
authors.lastname: Sardana
authors.forename: Janusz M
authors.initials: JM
authors.lastname: Bujnicki
authors.forename: Edward M
authors.initials: EM
authors.lastname: Marcotte
authors.forename: Arlen W
authors.initials: AW
authors.lastname: Johnson
mesh_terms: D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D001483:Base Sequence; D017124:Conserved Sequence; D017931:DNA Primers / Q000235:genetics; D019143:Evolution, Molecular; D017353:Gene Deletion; D005800:Genes, Fungal; D005816:Genetic Complementation Test; D007700:Kinetics; D008745:Methylation; D008780:Methyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D012323:RNA Processing, Post-Transcriptional; D012331:RNA, Fungal / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012337:RNA, Ribosomal, 18S / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism; D054682:Ribosome Subunits, Small, Eukaryotic / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D012331:RNA, Fungal; D012337:RNA, Ribosomal, 18S; C501334:RPS3 protein, S cerevisiae; D011993:Recombinant Fusion Proteins; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; C578381:Bud23 protein, S cerevisiae; D008780:Methyltransferases