The translational activator Sov1 coordinates mitochondrial gene expression with mitoribosome biogenesis

Area of Science:

• Molecular Biology
• Cellular Respiration
• Mitochondrial Genetics

Background:

• Mitoribosome biogenesis is crucial for cellular respiratory capacity, requiring coordinated expression of nuclear and mitochondrial genomes.
• The mitochondrion-encoded ribosomal protein Var1 (uS3m) is essential for mitoribosome function, particularly mRNA binding.
• Mechanisms regulating VAR1 gene expression and Var1 protein incorporation into mitoribosomes remain largely unknown.

Purpose of the Study:

• To elucidate the regulatory mechanisms governing the expression of the mitochondrion-encoded VAR1 mRNA.
• To identify factors involved in Var1 protein synthesis and its assembly into the mitochondrial small ribosomal subunit (mtSSU).
• To understand the role of Sov1 in Var1 expression and mitoribosome biogenesis.

Main Methods:

• Investigated the interaction between Sov1 and VAR1 mRNA.
• Analyzed the role of Sov1 in Var1 protein synthesis using biochemical assays.
• Studied the impact of Sov1 on the late stages of mitochondrial small ribosomal subunit assembly.

Main Results:

• Identified Sov1 as a bona fide translational activator of VAR1 mRNA.
• Demonstrated that Sov1 interacts with newly synthesized Var1 polypeptide.
• Showed Sov1 facilitates Var1 incorporation into the mtSSU, which is necessary for uS14 and mS46 assembly.

Conclusions:

• Sov1 plays a dual role: activating Var1 mRNA translation and assisting Var1 protein integration into the mitoribosome.
• A novel translational regulatory mechanism involving Sov1 fine-tunes Var1 synthesis for efficient mitoribosome assembly.
• This regulation is critical for maintaining cellular respiratory function through proper mitoribosome biogenesis.