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Has1p, a member of the DEAD‐box family, is required for 40S ribosomal subunit biogenesis in Saccharomyces cerevisiae †
Author(s) -
Emery Bertrand,
De La Cruz Jesús,
Rocak Sanda,
Deloche Olivier,
Linder Patrick
Publication year - 2004
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2003.03973.x
Subject(s) - eukaryotic small ribosomal subunit , biology , ribosome biogenesis , eukaryotic large ribosomal subunit , ribosomal rna , ribosomal protein , eukaryotic ribosome , ribosome , saccharomyces cerevisiae , genetics , 18s ribosomal rna , rna , gene
Summary The Has1 protein, a member of the DEAD‐box family of ATP‐dependent RNA helicases in Saccharomyces cerevisiae , has been found by different proteomic approaches to be associated with 90S and several pre‐60S ribosomal complexes. Here, we show that Has1p is an essential trans‐ acting factor involved in 40S ribosomal subunit biogenesis. Polysome analyses of strains genetically depleted of Has1p or carrying a temperature‐sensitive has1‐1 mutation show a clear deficit in 40S ribosomal subunits. Analyses of pre‐rRNA processing by pulse‐chase labelling, Northern hybridization and primer extension indicate that these strains form less 18S rRNA because of inhibition of processing of the 35S pre‐rRNA at the early cleavage sites A 0 , A 1 and A 2 . Moreover, processing of the 27SA 3 and 27SB pre‐rRNAs is delayed in these strains. Therefore, in addition to its role in the biogenesis of 40S ribosomal subunits, Has1p is required for the optimal synthesis of 60S ribosomal subunits. Consistent with a role in ribosome biogenesis, Has1p is localized to the nucleolus. On sucrose gradients, Has1p is associated with a high‐molecular‐weight complex sedimenting at positions equivalent to 60S and pre‐60S ribosomal particles. A mutation in the ATP‐binding motif of Has1p does not support growth of a has1 null strain, suggesting that the enzymatic activity of Has1p is required in ribosome biogenesis. Finally, sequence comparisons suggest that Has1p homologues exist in all eukaryotes, and we show that a has1 null strain can be fully complemented by the Candida albicans homologue.