Understanding the Assembly of the Small Ribosomal Subunit in Bacteria

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The ribosome catalyzes protein synthesis in bacterial cells. Proteins are the building blocks for cellular structures and also for the enzymes that perform the biochemical reactions necessary to sustain life. Considering our dependency from bacteria for production of food and biofuels and for manufacturing a large number of basic products for Canadians (antibiotics, vaccines, enzymes and chemicals for industry, etc), it is essential that key processes of the bacterial physiology, including the assembly of the ribosome, are well understood. Made of two subunits (called 30S and 50S) and containing more than 50 individual components, the ribosome constitutes one of the most intricate macromolecular machines found in living organisms. Previous studies from others and us have identified a number of protein factors that act at the late stages of assembly of the 30S subunit, making its maturation an extremely efficient process. However, their mechanisms of action have not been revealed. Our research program is aimed at establishing a functional model for four critical assembly factors, YjeQ, RbfA, RimM and Era. Earlier studies suggested that these factors act in concert during the late stages of maturation of the 30S subunit and that they constitute the main group of proteins boosting the efficiency of the assembly process. To this end, we are obtaining the cryo-electron microscopy structure of ribosome intermediates accumulated by single-gene deletion strains lacking these factors and will study their degree of structural similarity. Collectively, these structures will establish whether YjeQ, RbfA, RimM and Era act in the same or different stages of assembly. In addition, we will establish the specific order in which they bind to the 30S ribosomal subunit and the conformational changes that they induce. As our program progresses, we will study how additional assembly factors also assist the process of assembly and tune the function of YjeQ, RbfA, RimM and Era. Ultimately, the outcome of our research will delineate the sequence of events that made ribosome assembly a highly efficient process. Consequently, it will constitute a significant step forward in our understanding of one of the essential processes for life.