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Roles of the negatively charged N-terminal extension of Saccharomyces cerevisiae ribosomal protein S5 revealed by characterization of a yeast strain containing human ribosomal protein S5

¹ Department of Biological, Geological and Environmental Sciences, Cleveland State University, Cleveland, Ohio 44115, USA
² Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA
³ Department of Molecular Genetics, Microbiology and Immunology, Robert Wood Johnson Medical School, The University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey 08854, USA
⁴ Department of Nutrition, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA
⁵ Department of Microbiology and Immunology, Downstate Medical Center, State University of New York, Brooklyn, New York 11203, USA

Ribosomal protein (rp) S5 belongs to a family of ribosomal proteins that includes bacterial rpS7. rpS5 forms part of the exit (E) site on the 40S ribosomal subunit and is essential for yeast viability. Human rpS5 is 67% identical and 79% similar to Saccharomyces cerevisiae rpS5 but lacks a negatively charged (pI 3.27) 21 amino acid long N-terminal extension that is present in fungi. Here we report that replacement of yeast rpS5 with its human homolog yielded a viable yeast strain with a 20%–25% decrease in growth rate. This replacement also resulted in a moderate increase in the heavy polyribosomal components in the mutant strain, suggesting either translation elongation or termination defects, and in a reduction in the polyribosomal association of the elongation factors eEF3 and eEF1A. In addition, the mutant strain was characterized by moderate increases in +1 and –1 programmed frameshifting and hyperaccurate recognition of the UAA stop codon. The activities of the cricket paralysis virus (CrPV) IRES and two mammalian cellular IRESs (CAT-1 and SNAT-2) were also increased in the mutant strain. Consistently, the rpS5 replacement led to enhanced direct interaction between the CrPV IRES and the mutant yeast ribosomes. Taken together, these data indicate that rpS5 plays an important role in maintaining the accuracy of translation in eukaryotes and suggest that the negatively charged N-terminal extension of yeast rpS5 might affect the ribosomal recruitment of specific mRNAs.

Keywords: ribosomal protein S5(S7); E-site; eEF3; translation accuracy; IRES

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