Abstract #27

Functional specialization in the yeast ribosome revealed by high-resolution phenomics. Jonathan L.S. Esguerra, Jonas Warringer, Luciano Fernandez-Ricaud, Anders Blomberg. CMB-Microbiology, Lundberg Lab, Göteborg University, Göteborg, Sweden.
   Ribosomal protein genes belong to a distinct gene ontology category by virtue of their association with the ribosome. In terms of biological function, they are generally annotated as being involved in protein biosynthesis. However, reports on some ribosomal proteins acting “extra-ribosomally” are plentiful. This goes against the conventional view of r-proteins as mere accessory components of the ribosome, acting only either as architectural supports of the rRNA scaffold or performing their functions exclusively within the perimeters of the translational apparatus. In this study, we undertook a parallel analysis of the phenotypic profiles of non-essential core components of the cytoplasmic ribosome (110 rp genes) and a number of its transient residents (9 translational factors), during 38 environmental conditions, targeting various aspects of cellular physiology. The analysis of 20,000 growth curves, corresponding to 3 million individual growth measurements, revealed a surprising range of phenotypes ranging from extreme sensitivity to extreme resistance in essentially every tested environment. Identification of dominant trends within the plethora of phenotypes allowed for the separation of the ribosomal proteome into distinct functional groups. For instance, on one end we found distinct stress proteins which are completely dispensable for growth during optimal conditions but are required in many perturbed environments. On the other end are r-proteins belonging to the “turbo” class encompassing proteins dispensable for growth in stress environments but are required only when the whole cell machinery is engaged towards maximal growth and proliferation. Surprisingly, we also found that phenotypic concordance among the paralogous r-proteins was the exception rather than rule. In fact, paralogous r-proteins tended to display opposite phenotypes, even when sharing 100% sequence identity. Our study provided evidence for a previously unknown phenotypic diversity within the eukaryotic ribosome, suggesting a high degree of r-protein functional specialization.

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