The translational activator Sov1 coordinates mitochondrial gene expression with mitoribosome biogenesis

Abstract

<jats:title>Abstract</jats:title> <jats:p>Mitoribosome biogenesis is an expensive metabolic process that is essential to maintain cellular respiratory capacity and requires the stoichiometric accumulation of rRNAs and proteins encoded in two distinct genomes. In yeast, the ribosomal protein Var1, alias uS3m, is mitochondrion-encoded. uS3m is a protein universally present in all ribosomes, where it forms part of the small subunit (SSU) mRNA entry channel and plays a pivotal role in ribosome loading onto the mRNA. However, despite its critical functional role, very little is known concerning VAR1 gene expression. Here, we demonstrate that the protein Sov1 is an in bona fide VAR1 mRNA translational activator and additionally interacts with newly synthesized Var1 polypeptide. Moreover, we show that Sov1 assists the late steps of mtSSU biogenesis involving the incorporation of Var1, an event necessary for uS14 and mS46 assembly. Notably, we have uncovered a translational regulatory mechanism by which Sov1 fine-tunes Var1 synthesis with its assembly into the mitoribosome.</jats:p>

The Mitogenomes of Ophiostoma minus and Ophiostoma piliferum and Comparisons With Other Members of the Ophiostomatales

“…For the latter, such as in some members of the Capnodiales, Wai et al (2019) identified a nuclear-encoded ortholog of the mitochondrial-encoded version of rps3 . Among the metazoans and the fungi, the nuclear and mitochondrial versions of rps3 have been shown to be required for initiating protein translation and appear to have “moonlighting activities” by being involved in DNA repair, cell signaling, apoptosis, and potentially in gene regulation ( Neu et al, 1998 ; Kim et al, 2013 ; Wang et al, 2019 ; Seshadri et al, 2020 ). Maintaining the rps3 gene within the rnl group I intron might be a fortuitous association that provides the rps3 gene a locus embedded within an essential gene ( rnl ) presumable transcribed at a high rate, and this may “protect” the intron from being eroded by drift.…”

Molecular Connectivity of Mitochondrial Gene Expression and OXPHOS Biogenesis

“…These analyses revealed a heterogeneous group of proteins, most of which are directly involved in mitochondrial translation (Figure 4B). Along with nearby SSU proteins, we identified multiple translational activators, including Pet111 (Green-Willms et al, 2001), Pet54 (Naithani et al, 2003), Sov1 (Seshadri et al, 2020), Cbs2 (Muroff and Tzagoloff, 1990;Rö del, 1986), and Aep1 (Payne et al, 1991(Payne et al, , 1993, which are specific for translation of COX2, COX3, VAR1, COB, and ATP9 mRNAs, respectively. Moreover, other proteins involved in translation were found, namely, Aim23, the mitochondrial IF3 (Kuzmenko et al, 2016), and Msc6, a PPR protein suggested to play a role in translation initiation (Franco et al, 2019).…”

The mitospecific domain of Mrp7 (bL27) supports mitochondrial translation during fermentation and is required for effective adaptation to respiration

“…Var1 is a mtDNA-encoded component of the mtSSU, and thus a decrease in its synthesis in turn potentially may compromise mitoribosomal function. Allotopic expression of a universal Var1 (Var1 u ) protein (i.e., as a functional chimera with a mitochondrial targeting signal) ( Seshadri et al. , 2020 ) did not restore the translational capacity of glucose-grown mrp7 (1-187) and mrp7 (1-146) cells, indicating that the mtVar1 levels were not the limiting factor for mitotranslation in these mutants under fermentation conditions (Supplemental Figure S5).…”

“…A mitochondrially targeted universal Var1 derivative (Var1 u ) was expressed in the indicated strains using the pRS316- VAR1 u plasmid ( Sanchirico et al. , 1995 ; Seshadri et al. , 2020 ).…”

“…Deletions in the C-terminal ORF (while maintaining integrity of cloned 3' non-coding region) were generated using a PCR-mediated deletion of pRS413-MRP7 plasmid DNA (Hansson et al, 2008). A mitochondrially targeted universal Var1 derivative (Var1 u ) was expressed in indicated strains using the pRS316-VAR1 u plasmid (Sanchirico et al, 1995;Seshadri et al, 2020). Mrp7 wild type and mrp7 mutant strains, which also were deficient in MAM33 (Δmam33; MAM33::URA3), were created through homologous recombination of the URA3 marker to delete the entire MAM33 ORF in the Mrp7/mrp7 mutant strains.…”