The lateral stalk of ribosomes constitutes the GTPase-associated center and is responsible for recruiting translation factors to the ribosomes. The eukaryotic stalk contains a P-complex, in which one molecule of uL10 (formerly known as P0) protein binds two copies of P1/P2 heterodimers. Unlike bacterial uL10, eukaryotic uL10 has an extended protuberant (uL10ext) domain inserted into the N-terminal RNA-binding domain. Here, we determined the solution structure of the extended protuberant domain of Bombyx mori uL10 by nuclear magnetic resonance spectroscopy. Comparison of the structures of the B. mori uL10ext domain with eRF1-bound and eEF2-bound ribosomes revealed significant structural rearrangement in a "hinge" region surrounding Phe183, a residue conserved in eukaryotic but not in archaeal uL10. 15N relaxation analyses showed that residues in the hinge region have significantly large values of transverse relaxation rates. To test the role of the conserved phenylalanine residue, we created a yeast mutant strain expressing an F181A variant of uL10. An in vitro translation assay showed that the alanine substitution increased the level of polyphenylalanine synthesis by ∼33%. Taken together, our results suggest that the hinge motion of the uL10ext domain facilitates the binding of different translation factors to the GTPase-associated center during protein synthesis.