Mitochondrial NAD kinase Pos5 is required for CoQ biosynthesis in yeasts.
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S. pombe Δpos5 has 0.2-fold of wild-type CoQ10.
"CoQ levels in the Δpos5 strain of our construct were decreased to 0.2-fold of those in the wild-type strain"
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The CoQ decrease is not explained by respiratory deficiency, because a cytochrome c mutant has near-normal CoQ.
"The Δcyc1 strain did not show a marked decrease in CoQ levels, suggesting that respiratory deficiency alone does not account for the low CoQ level in the Δpos5 strain."
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Δpos5 cannot use non-fermentable carbon, is H2O2-sensitive and grows slowly on minimal medium.
"The Δpos5 strain failed to grow on YEGES medium containing glycerol and ethanol as non-fermentable carbon sources and showed retarded growth on YES containing hydrogen peroxide as well as on minimal medium"
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S. cerevisiae POS5 complements the S. pombe Δpos5 CoQ defect.
"CoQ levels in the NSP7 strain were recovered to 0.9-fold of that observed in the Δpos5 + pos5 strain (NSP11)"
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Mitochondrial NADP+ and total NADP(H) are reduced in S. pombe Δpos5.
"Mitochondrial NADP+ level and total NADP(H) level in Δpos5 were decreased to 0.6- and 0.8-fold, respectively, of those in the wild-type strain"
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Plasmid-expressed Pos5-GFP co-localises with MitoTracker, whereas the endogenous C-terminal GFP fusion is mislocalised and non-functional.
"The Pos5-GFP fluorescence overlapped with the MitoTracker Red FM signal (Fig 5), indicating that Pos5 localizes to mitochondria as a mitochondrial NAD(H) kinase"
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Only a mitochondrially targeted NAD kinase rescues CoQ in Δpos5. A Pos5 lacking its first 83 residues and cytosolic Utr1 do not.
"CoQ quantification showed that only MTS36UTR1 restored CoQ production, whereas neither ΔMTS83pos5 nor UTR1 could recover CoQ levels in the Δpos5 strain"
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Overexpressing coq6 does not restore CoQ in Δpos5, so Coq6 is not the limiting step.
"However, CoQ levels in the Δpos5 strain overexpressing coq6 were comparable to that in the Δpos5 strain integrating a vector"
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PHB partially restores CoQ in Δpos5.
"Supplementation of 0.5 mM PHB partially increased CoQ levels in the Δpos5 strain compared to the untreated condition"
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The S. cerevisiae pos5 deletion also has 0.2-fold of wild-type CoQ6.
"CoQ6 levels in ΔScpos5 were decreased to 0.2-fold of those in the wild-type strain"
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The NADPH-dependent reaction(s) that link Pos5 to CoQ synthesis are not identified.
"Our results suggest that the requirement for NADPH lies in the synthesis of the precursor of CoQ biosynthesis, although more detailed analysis is necessary to define the specific reaction(s) that depend on mitochondrial NADPH."