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Molecular and Cellular Biology, February 2000, p. 1370-1381, Vol. 20, No. 4
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Spb1p Is a Yeast Nucleolar Protein Associated with Nop1p and Nop58p That Is Able To Bind S-Adenosyl-L-Methionine In Vitro

Lionel Pintard,1 Dieter Kressler,2 and Bruno Lapeyre1,*

Centre de Recherche de Biochimie Macromoléculaire du CNRS, 34293 Montpellier, France,1 and Centre Médical Universitaire, Université de Genève, CH-1211 Geneva, Switzerland2

Received 26 July 1999/Returned for modification 9 September 1999/Accepted 10 November 1999

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 [3H]AdoMet in vitro, suggesting that it is a novel methylase, whose possible substrates will be discussed.

* Corresponding author. Mailing address: CRBM, 1919 Route de Mende, 34293 Montpellier Cedex 5, France. Phone: 33-467-61-36-80. Fax: 33-467-04-02-31. E-mail: lapeyre{at}crbm.cnrs-mop.fr.

Molecular and Cellular Biology, February 2000, p. 1370-1381, Vol. 20, No. 4
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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