Prefabrication of a ribosomal protein subcomplex essential for eukaryotic ribosome formation.

Spatial clustering of ribosomal proteins (r-proteins) through tertiary interactions is a striking structural feature of the eukaryotic ribosome. However, the functional importance of these intricate inter-connections, and how they are established is currently unclear. Here, we reveal that a conserved ATPase, Fap7, organizes interactions between neighboring r-proteins uS11 and eS26 prior to their delivery to the earliest ribosome precursor, the 90S. In vitro, uS11 only when bound to Fap7 becomes competent to recruit eS26 through tertiary contacts found between these r-proteins on the mature ribosome. Subsequently, Fap7 ATPase activity unloads the uS11:eS26 subcomplex onto its rRNA binding site, and therefore ensures stoichiometric integration of these r-proteins into the 90S. Fap7-depletion in vivo renders uS11 susceptible to proteolysis, and precludes eS26 incorporation into the 90S. Thus, prefabrication of a native-like r-protein subcomplex drives efficient and accurate construction of the eukaryotic ribosome.

Roles of ribosomal proteins in the functioning of translational machinery of eukaryotes.

Ribosomal proteins (rps) are constituents of ribosomal subunits together with the rRNAs, and the work of the ribosomes is based on highly cooperative interactions involving these biopolymers. Eukaryotic ribosomal subunits contain proteins that have bacterial counterparts as well as proteins specific only to eukaryotes and archaea and proteins unique to eukaryotes. Roles of eukaryotic rps in functioning of the translation machinery are studied in less detail than those of bacterial ones. However, application of various structural, biochemical and genetic approaches made it possible to obtain data suggesting implication of many particular eukaryotic rps in binding of participants of translation process (ribosomal ligands). Here we present a review on these data as well as their analysis aimed to reveal conserved and eukaryote-specific functions of eukaryotic rps in the work of translational machinery.