Analysis of chimeric ribosomal stalk complexes from eukaryotic and bacterial sources: structural features responsible for specificity of translation factors.

Ribosomal protein P0 forms a pentameric complex with two heterodimers of the flexible stalk proteins P1•P2 and plays a role in the functional interaction of eukaryotic ribosomes with translational factors. To investigate the functionality of domains of P0 characteristic to eukaryotes, we constructed various chimeras between silkworm P0 and Escherichia coli counterpart L10. Replacement of the C-terminal region of L10 with that of P0 allowed the binding of two P1•P2 heterodimers, which supported ribosomal activity dependent on eukaryotic elongation factors eEF-2/eEF-1α, but not activity dependent on bacterial factors EF-G/EF-Tu. Conversely, replacement of the C-terminal region of P0 with that of L10 allowed binding of two bacterial L12 homodimers, which resulted in a low level of activity dependent on bacterial factors. Insertion of the extended region of P0 that is absent in the bacterial counterpart into L10 did not affect L12 binding or bacterial factor-dependent activity, but deletion of this region from P0 resulted in a 40% reduction in eukaryotic factor-dependent activity. The results indicate that the C-terminal regions of P0 and L10 are responsible for binding of the cognate stalk dimers and ribosomal specificity for translation factors and suggest that the extended region participates in accessibility only for eukaryotic factors.