<p>Ribosome assembly is a complex process, facilitated by more than 20 protein factors in bacteria. GTPases and ATPases represent the energy driving force of these factors. In my research as a PhD student, I studied the function of two GTPases, YjeQ and RbgA, involved in the assembly of the small and the large ribosomal subunits, respectively.</p> <p>We isolated and characterized <em>in-vivo</em> assembled immature small (30S) and large (50S) subunits using a perturbation in the genes coding for these proteins. We observed that both subunits contained an incomplete ribosomal protein content, mainly lacking late-binding r-proteins. Additionally, we observed distortions in the functional core of the immature ribosomal subunit, particularly in the mRNA decoding center of the 30S subunit, the peptidyltransferase center of the 50S subunit, and tRNA binding sites.</p> <p>Additionally, we have determined that the YjeQ protein interacts with the 30S subunit through its N-terminal OB-fold domain, and C-terminal Zn-finger motif. The binding site of YjeQ on the 30S subunit prevents the interaction with tRNAs, translation factors, and the 50S subunit.</p> <p>Finally, we uncovered a novel functional interplay between RbgA and the ribosomal protein L16 during late stages of ribosomal assembly. We proposed that recruitment of L16 to the assembling 50S subunit would induce a conformational rearrangement that would ultimately promote the GTP-dependent release of RbgA.</p> <p>The function of the assembly factors associated with the process of <em>in-vivo</em> ribosome assembly is not known, and thus a framework on how ribosomes are built is still elusive. I believe the research presented in this thesis provides novel insights into the role of YjeQ and RbgA in the assembly of ribosomes</p> / Doctor of Philosophy (PhD)