Partial suppression of the respiratory defect of qrs1/her2 glutamyl-tRNA amidotransferase mutants by overexpression of the mitochondrial pentatricopeptide Msc6p

Abstract

Recently, a large body of evidences indicates the existence in the mitochondrial matrix of foci that contain different proteins involved in mitochondrial RNA metabolism. Some of these proteins have a pentatricopeptide repeat motif that constitutes their RNA-binding structures. Here we report that MSC6, a mitochondrial pentatricopeptide protein of unknown function, is a multi copy suppressor of mutations in QRS1/HER2 a component of the trimeric complex that catalyzes the transamidation of glutamyl-tRNAQ to glutaminyl-tRNAQ. This is an essential step in mitochondrial translation because of the lack of a specific mitochondrial aminoacyl glutaminyl-tRNA synthetase. MSC6 over-expression did not abolish translation of an aberrant variant form of Cox2p detected in QRS1/HER2 mutants, arguing against a suppression mechanism that bypasses Qrs1p function. A slight decrement of the mitochondrial translation capacity as well as diminished growth on respiratory carbon sources media for respiratory activity was observed in the msc6 null mutant. Additionally, the msc6 null mutant did not display any impairment in RNA transcription, processing or turnover. We concluded that Msc6p is a mitochondrial matrix protein and further studies are required to indicate the specific function of Msc6p in mitochondrial translation.

Msc6p is required for mitochondrial translation initiation in the absence of formylated Met‐tRNAfMet

“…Msc6p belongs to the large pentatricopeptide protein family whose members have been shown to interact with and stabilize RNA . Previous studies indicated that ,mutations in MSC6 did not affect transcription, processing or stability of mitochondrial RNAs but did marginally reduce mitochondrial translation . These observations together with the respiratory‐deficient phenotype of the fmt1 msc6 double mutant, suggested a role of Msc6p in mitochondrial protein synthesis.…”

“…The suppressor properties of MSC6 overexpression over mitochondrial translation defective mutants lead us to investigate putative interactions of MSC6 with other mitochondrial translation mutants, such as fmt1 , msi1 , trm1 , pus5 , oms1 , etc. that were already described in a high throughput study .…”

“…MSC6 overexpression was reported to suppress some qrs1/her2 mutants lacking the amidotransferase (AdT) necessary for converting Glu‐tRNA Gln to Gln‐tRNA Gln . Although EF‐Tu can discriminate mischarged tRNAs, it is not full‐proof when the mischarged tRNA is present in excess .…”

“…Mutations in MSC6 were first shown to promote unequal chromatid recombination during meiosis . Subsequently, Msc6p was found to be a mitochondrial matrix protein, which when overexpressed, suppresses impaired mitochondrial translation in qrs1 / her2 mutants . Msc6p, like Aep3p and Rmd9p, contains an RNA‐binding groove formed by a pentatricopeptide repeat (PPR) motif consisting of a degenerate 35 amino acid sequence repeated in tandem in two antiparallel α‐helices leading to a helix‐turn‐helix domain.…”

Aep3p-dependent translation of yeast mitochondrialATP8

“…PPR proteins have been described in chloroplasts and in plant, human, and fungal mitochondria (Shikanai, 2006; Lipinski et al , 2011; Solotoff et al , 2015). Pet309p, Atp22p, and Msc6p are examples of yeast mitochondrial PPR proteins involved in the stability and/or translation of mitochondrially encoded RNAs (Krause et al , 2004; Zeng et al , 2007; Moda et al , 2016). Like other PPR proteins, Aep3p was recently shown to cosediment with mitochondrial ribosomes in a large complex termed Miorex (Kehrein et al , 2015).…”