<p>Strain list.</p>

Coenzyme Q (CoQ) is an essential component of the electron transport chain, and ten genes involved in CoQ biosynthesis have been identified in Schizosaccharomyces pombe. To gain further insight into CoQ biosynthesis, we screened the Bioneer gene-deletion library and found that the Δpos5 strain produced only 0.2-fold of the wild-type CoQ10 level. Pos5 shares homology with Saccharomyces cerevisiae Pos5 (ScPos5), a mitochondrial NADH (or NAD+) kinase that generates NADPH (or NADP+). Heterologous expression of ScPOS5 in the S. pombe Δpos5 strain recovered CoQ content to 0.9-fold of the wild-type level, indicating functional conservation of Pos5 between the two yeasts. Consistently, CoQ6 level in ΔScpos5 was decreased to 0.2-fold of that in the wild-type strain. The Δpos5 strain exhibited several phenotypes characteristic of CoQ-deficient S. pombe, including inability to grow on non-fermentable carbon sources, hypersensitivity to oxidative stress, and high sulfide production. Among CoQ biosynthetic enzymes, Coq6 monooxygenase is thought to utilize NADPH. Supplementation with VA or PHB partially restored CoQ production in the Δpos5 strain, while overexpression of coq6 had negligible effect. These findings suggest that Pos5 is required for the earlier step of CoQ biosynthesis.辅酶Q(Coenzyme Q, CoQ)是电子传递链的必需组分，目前已在粟酒裂殖酵母(Schizosaccharomyces pombe)中鉴定出10个参与CoQ生物合成的基因。为进一步解析CoQ的生物合成机制，我们对Bioneer基因缺失文库进行了筛选，发现Δpos5菌株的CoQ10水平仅为野生型的0.2倍。Pos5与酿酒酵母(Saccharomyces cerevisiae)的Pos5（ScPos5）具有同源性，后者是一种可生成烟酰胺腺嘌呤二核苷酸磷酸（NADPH）或烟酰胺腺嘌呤二核苷酸磷酸（NADP+）的线粒体烟酰胺腺嘌呤二核苷酸（NADH）/烟酰胺腺嘌呤二核苷酸（NAD+）激酶。在粟酒裂殖酵母Δpos5菌株中异源表达ScPOS5可将CoQ含量恢复至野生型水平的0.9倍，表明两种酵母中Pos5的功能具有保守性。与之一致的是，ΔScpos5菌株中的CoQ6水平降至野生型菌株的0.2倍。Δpos5菌株表现出多种CoQ缺陷型粟酒裂殖酵母的典型表型，包括无法在非发酵碳源上生长、对氧化应激高度敏感以及硫化物生成量升高。在CoQ生物合成酶类中，Coq6单加氧酶被认为可利用NADPH。向Δpos5菌株中添加VA或PHB可部分恢复其CoQ合成能力，而过表达coq6则几乎无效果。上述研究结果表明，Pos5是CoQ生物合成早期步骤所必需的因子。