Spb1p is a yeast nucleolar protein associated with Nop1p and Nop58p that is able to bind S-adenosyl-L-methionine in vitro.
We present here the characterization of SPB1, an essential yeast gene that is required for ribosome synthesis. A cold-sensitive allele for that gene (referred to here as spb1-1) had been previously isolated as a suppressor of a mutation affecting the poly(A)-binding protein gene (PAB1) and a thermosensitive allele (referred to here as spb1-2) was isolated in a search for essential genes required for gene silencing in Saccharomyces cerevisiae. The two mutants are able to suppress the deletion of PAB1, and they both present a strong reduction in their 60S ribosomal subunit content. In an spb1-2 strain grown at the restrictive temperature, processing of the 27S pre-rRNA into mature 25S rRNA and 5.8S is completely abolished and production of mature 18S is reduced, while the abnormal 23S species is accumulated. Spb1p is a 96.5-kDa protein that is localized to the nucleolus. Coimmunoprecipitation experiments show that Spb1p is associated in vivo with the nucleolar proteins Nop1p and Nop5/58p. Protein sequence analysis reveals that Spb1p possesses a putative S-adenosyl-L-methionine (AdoMet)-binding domain, which is common to the AdoMet-dependent methyltransferases. We show here that Spb1p is able to bind [(3)H]AdoMet in vitro, suggesting that it is a novel methylase, whose possible substrates will be discussed.
Pintard
L
L
Centre de Recherche de Biochimie Macromoléculaire du CNRS, 34293 Montpellier, France.
Kressler
D
D
Lapeyre
B
B
D000483:Alleles; D000595:Amino Acid Sequence; D001483:Base Sequence; D017124:Conserved Sequence; D017931:DNA Primers / Q000235:genetics; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D005800:Genes, Fungal; D005816:Genetic Complementation Test; D008780:Methyltransferases; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D039102:Poly(A)-Binding Proteins; D011485:Protein Binding; D012323:RNA Processing, Post-Transcriptional; D012331:RNA, Fungal / Q000096:biosynthesis; D012335:RNA, Ribosomal / Q000096:biosynthesis; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism*; D020718:Ribonucleoproteins, Small Nucleolar; D012436:S-Adenosylmethionine / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D013489:Suppression, Genetic; D013696:Temperature
D017931:DNA Primers; D005656:Fungal Proteins; C064793:NOP1 protein, S cerevisiae; C438199:NOP58 protein, S cerevisiae; D009687:Nuclear Proteins; D039102:Poly(A)-Binding Proteins; D012331:RNA, Fungal; D012335:RNA, Ribosomal; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; D020718:Ribonucleoproteins, Small Nucleolar; D029701:Saccharomyces cerevisiae Proteins; D012436:S-Adenosylmethionine; D008780:Methyltransferases; C403804:SPB1 protein, S cerevisiae