Article

Yeast ribosomal protein L40 assembles late into pre-60S ribosomes and is required for their cytoplasmic maturation.

University of Seville, Spain
Journal of Biological Chemistry (Impact Factor: 4.6). 09/2012; DOI: 10.1074/jbc.M112.400564
Source: PubMed

ABSTRACT Most ribosomal proteins play important roles in ribosome biogenesis and function. Herein, we have examined the contribution of the essential ribosomal protein L40 in these processes in the yeast Saccharomyces cerevisiae. Deletion of either the RPL40A or RPL40B gene and in vivo depletion of L40 impair 60S ribosomal subunit biogenesis. Polysome profile analyses reveal the accumulation of half-mers and a moderate reduction in free 60S ribosomal subunits. Pulse-chase, northern blotting and primer extension analyses in the L40-depleted strain clearly indicate that L40 is not strictly required for the pre-rRNA processing reactions but contributes to optimal 27SB pre-rRNA maturation. Moreover, depletion of L40 hinders the nucleo-cytoplasmic export of pre-60S ribosomal particles. Importantly, all these defects most likely appear as the direct consequence of impaired Nmd3 and Rlp24 release from cytoplasmic pre-60S ribosomal subunits and their inefficient recycling back into the nucle(ol)us. In agreement, we show that hemagglutinin epitope-tagged L40A assembles in the cytoplasm into almost mature pre-60S ribosomal particles. Finally, we have identified that the hemagglutinin epitope-tagged L40A confers resistance to sordarin, a translation inhibitor that impairs the function of eukaryotic elongation factor 2, while the rpl40a and rpl40b null mutants are hypersensitive to this antibiotic. We conclude that L40 is assembled at a very late stage into pre-60S ribosomal subunits and that its incorporation into 60S ribosomal subunits is a prerequisite for subunit joining and may ensure proper functioning of the translocation process.

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