Poster abstracts

Poster number 28 submitted by Arnab Ghosh

Eukaryotic ribosomal protein S5 - a docking site for initiation factor eIF2?

Arnab Ghosh (Department of Biological, Geological and Environmental Sciences, Cleveland State University), Amber A. Bentley (Department of Biological, Geological and Environmental Sciences, Cleveland State University), Thomas Lumsden (Department of Biological, Geological and Environmental Sciences, Cleveland State University), Anton A. Komar (Department of Biological, Geological and Environmental Sciences, Cleveland State University)

Abstract:
Despite a large body of information provided by X-ray analysis of prokaryotic ribosomes, the role of many prokaryotic ribosomal proteins remains rather obscure. Even less is known about the functions of eukaryotic ribosomal proteins. Many eukaryotic proteins have evolved additional segments, the function(s) of which are not quite clear, but may be related to the differences in translation machineries between different kingdoms. Very little is also known about the position of initiation factors on the surface of the 40S subunit and in particular the role of ribosomal proteins in recruiting these factors. Ribosomal protein (rp) S5 belongs to a family of conserved ribosomal proteins that includes bacterial rpS7. The protein forms part of the exit (E) site on the 30S/40S ribosomes and contributes to the formation of the mRNA exit channel. rpS5/7 proteins possess a conserved central/C-terminal region and variable N-terminal ends. Many eukaryotes and in particular fungi have evolved a longer rpS5 protein with substantial N-terminal extension (>50 aa). To investigate the function of the yeast rpS5 and in particular the role of its N-term region, we obtained and characterized yeast strains in which the wt yeast rpS5 was replaced by its truncated variants, lacking 13, 24, 30 and 46 N-terminal amino acids, respectively. All mutant yeast strains were viable and displayed only moderately reduced growth rates, with the exception of the strain lacking 46 N-terminal amino acids, which had a doubling time of about 3 hours. Biochemical analysis of the mutant yeast strains suggests that the N-terminal part of the eukaryotic and in particular yeast rpS5 may impact the ability of 40S subunits to function properly in translation and affects the efficiency and accuracy of initiation process, in particular, increasing the affinity of eIF2 to mutant 40S ribosomes. We hypothesize that N-terminal extension of eukaryotic ribosomal protein S5 has evolved to control the interaction of eukaryotic initiation factor 2 (and perhaps some other factors) with the 40S ribosome.

Keywords: Ribosomal protein S5, translation, eIF2