Non-Coding Elements Can Influence Ribosomal Protein Functions and the Composition of Assembled Ribosomes

“Ribosome code” hypothesis proposes ribosomes composed of different ribosomal protein paralogs might govern distinct functions. Identification of the regulatory elements likely involved in controlling ribosomal protein functions and the distinct composition of the correspondingly assembled paralog-specific ribosomes should be informative to this phenomenon. Here we show that modulation of different RPL36 non-coding elements can influence protein functions independently of the protein abundance. This is manifested by distinct growth rate, differential biogenesis of the 60S ribosomal subunits, and characteristic composition of the purified translating ribosomes. Proteomic analysis of highly purified paralog-specific ribosomes from strain co-expressing identical Arabidopsis RPL36B proteins from two different constructs reveals their unique composition as two distinctive classes of ribosomes characterized by specifically-enriched components. This observation is remarkably analogous to the composition of endogenous RPL36 paralog-specific ribosomes. The proposed mechanism underlying functional distinction between ribosomal protein paralogs and the significance of evolving paralog-specific ribosomes are presented.