The N-terminal region of yeast mitoribosomal Mrp7/bL27m protein serves to optimize translation of nascent chains competent for OXPHOS complex assembly.

Abstract

The extreme N-terminal residues of the mitochondrial ribosomal bL27m proteins reside within the ribosomal peptidyl transferase center (PTC) and are conserved from their bacterial ancestors. Mutation or truncation of the N-terminal region of the yeast Mrp7/bL27m protein did not inhibit protein synthesis but significantly impacted the efficacy of the mitochondrial translational process with respect to yielding proteins competent to assemble into functional oxidative phosphorylation enzymes. The requirement for the N-terminal residues of Mrp7/bL27m to support normal mitotranslation wasmore apparent under respiratory growth. We demonstrate that the N-terminal region of Mrp7/bL27m impacts the environment of the PTC and speculate the bL27m proteins serve to fine-tune and optimize mitoribosomal activity with respect to the downstream fate of the nascent chain.