title: Yeast 18 S rRNA is directly involved in the ribosomal response to stringent AUG selection during translation initiation.
abstract: In eukaryotes, the 40 S ribosomal subunit serves as the platform of initiation factor assembly, to place itself precisely on the AUG start codon. Structural arrangement of the 18 S rRNA determines the overall shape of the 40 S subunit. Here, we present genetic evaluation of yeast 18 S rRNA function using 10 point mutations altering the polysome profile. All the mutants reduce the abundance of the mutant 40 S, making it limiting for translation initiation. Two of the isolated mutations, G875A, altering the core of the platform domain that binds eIF1 and eIF2, and A1193U, changing the h31 loop located below the P-site tRNA(i)(Met), show phenotypes indicating defective regulation of AUG selection. Evidence is provided that these mutations reduce the interaction with the components of the preinitiation complex, thereby inhibiting its function at different steps. These results indicate that the 18 S rRNA mutations impair the integrity of scanning-competent preinitiation complex, thereby altering the 40 S subunit response to stringent AUG selection. Interestingly, nine of the mutations alter the body/platform domains of 18 S rRNA, potentially affecting the bridges to the 60 S subunit, but they do not change the level of 18 S rRNA intermediates. Based on these results, we also discuss the mechanism of the selective degradation of the mutant 40 S subunits.
authors.affiliation: Molecular Cellular and Developmental Biology Program, Kansas State University, Manhattan, Kansas 66506, USA.
authors.forename: Naoki
authors.initials: N
authors.lastname: Nemoto
authors.forename: Chingakham Ranjit
authors.initials: CR
authors.lastname: Singh
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Udagawa
authors.forename: Suzhi
authors.initials: S
authors.lastname: Wang
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Thorson
authors.forename: Zachery
authors.initials: Z
authors.lastname: Winter
authors.forename: Takahiro
authors.initials: T
authors.lastname: Ohira
authors.forename: Miki
authors.initials: M
authors.lastname: Ii
authors.forename: Leos
authors.initials: L
authors.lastname: Valásek
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Brown
authors.forename: Katsura
authors.initials: K
authors.lastname: Asano
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D018387:Codon, Initiator / Q000378:metabolism*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D017354:Point Mutation; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012331:RNA, Fungal; D012337:RNA, Ribosomal, 18S / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D054682:Ribosome Subunits, Small, Eukaryotic / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism
chemical_list: D018387:Codon, Initiator; D021122:Protein Subunits; D012331:RNA, Fungal; D012337:RNA, Ribosomal, 18S