Molecular Wiring of a Mitochondrial Translational Feedback Loop

Area of Science:

• Mitochondrial biology
• Molecular genetics
• Cellular respiration

Background:

• The mitochondrial oxidative phosphorylation system requires coordinated gene expression from both nuclear and mitochondrial genomes.
• Feedback loops regulate the synthesis of mitochondrial-encoded subunits, crucial for complex assembly.

Purpose of the Study:

• To investigate the regulatory mechanism controlling the synthesis of cytochrome b, a key subunit of mitochondrial complex III.
• To elucidate the role of translational activators in coordinating mitochondrial protein synthesis with assembly efficiency.

Main Methods:

• Studied the function of translational activators Cbp3-Cbp6 and Cbs1 in regulating cytochrome b synthesis.
• Investigated the interaction of these activators with the cytochrome b-encoding mRNA at the mitoribosomal tunnel exit.

Main Results:

• Identified a molecular rheostat mechanism involving Cbp3-Cbp6 and Cbs1 at the mitoribosomal tunnel exit.
• Demonstrated that Cbs1 represses cytochrome b translation by sequestering mRNA during complex III assembly.
• Showed that Cbp3-Cbp6 binding releases the mRNA, allowing cytochrome b synthesis after complex assembly.

Conclusions:

• Established a feedback loop mechanism that links translational output to assembly efficiency for mitochondrial-encoded proteins.
• The study reveals the molecular wiring controlling cytochrome b synthesis, ensuring proper function of mitochondrial complex III.