Ribosome associated proteome analysis during quiescence and translational reactivation after a nutrient stimuli in Saccharomyces cerevisiae

CLARA SOLARI; PAULA PORTELA

Congreso; International Specialized Symposium in Yeasts ISSY 34; 2018

Saccharomyces cerevisiae enters quiescence when nutrients are consumed and re-enters cell cycle when nutrients are once again available. Changes in cell cycle are modulated through variations in cellular proteome at a given time; how translational regulation is achieved is our research goal. To characterize the translational machinery in monosomal or polysomal fractions of stationary phase (SP) wild type cells or after 30 or 60 minutes of fresh media addition we used nano-LC MS/MS and protein abundance estimations using exponentially modified protein abundance index (emPAI). In SP global translation is inactivated, after 30 min of fresh media addition global translation is still not fully recovered, while after 60 min polysome profiles are similar to an exponential phase. Proteomic analysis showed several proteins other than that involved in translation and protein folding interacting with ribosomes. Monosomes -but not polysomes- in all conditions present a subset of proteins involved in protein degradation. Enrichment analysis pointed to 30 min not as an intermediate condition but as a regulatory one, highly enriched in proteins involved with isoleucine and aromatic amino acid processes. We found a subset of small and large ribosomal subunits present only in the monosome in SP, such as Rpl31B and Rps0B. Protein abundance analyses showed that Stm1, a protein required for proper translation during stress, and that chaperons like Ssb1 and Ssb2 are associated to monosomes in SP. Moreover, polysomes in SP have translation elongation factors and the association of these factors diminishes along the stimuli. Hsp26 is associated to monosomes no matter the nutrient condition and is not present in polysomes. Taken together, our results shed light into translation control regulation by nutrient signalling and suggest how quiescent yeast cells can modify the translational machinery through ribosomal core modifications and/or auxiliary proteins factors association.