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Reference: Ray P, et al. (2008) The Saccharomyces cerevisiae 60 S Ribosome Biogenesis Factor Tif6p Is Regulated by Hrr25p-mediated Phosphorylation. J Biol Chem 283(15):9681-91

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Abstract

The biosynthesis of 60S ribosomal subunits in Saccharomyces cerevisiae requires Tif6p, the yeast homologue of mammalian eIF6. This protein is necessary for the formation of 60S ribosomal subunits because it is essential for the processing of 35S pre-rRNA to the mature 25S and 5.8S rRNAs. In the present work, using molecular genetic and biochemical analyses, we show that Hrr25p, an isoform of yeast casein kinase I, phosphorylates Tif6p both in vitro and in vivo. Tryptic phosphopeptide mapping of in vitro phosphorylated Tif6p by Hrr25p and 32P-labeled Tif6p isolated from yeast cells followed by mass spectrometric analysis revealed that phosphorylation occurred on a single tryptic peptide at Serine-174. Sucrose gradient fractionation as well as coimmunoprecipitation experiments demonstrated that a small but significant fraction of Hrr25p is bound to the 66S pre-ribosomal particles that also contain bound Tif6p. Depletion of Hrr25p from a conditional yeast mutant that fails to phosphorylate Tif6p was unable to process pre-rRNAs efficiently resulting in significant reduction in the formation of 25S rRNA. These results, along with our previous observations that phosphorytable serine-174 is required for yeast cell growth and viability, suggest that Hrr25p-mediated phosphorylation of Tif6p plays a critical role in the biogenesis of 60S ribosomal subunits in yeast cells.

Reference Type
Journal Article
Authors
Ray P, Basu U, Ray A, Majumdar R, Deng H, Maitra U
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