Shavlovskiĭ G M, Sibirnyĭ A A, Fedorovich D V, Seniuta E Z
Mikrobiologiia. 1982 Jan-Feb;51(1):96-101.
A positive method is proposed for selecting Pichia guilliermondii mutants with derepressed GTP cyclohydrolase. Mutants with the incompletely blocked gene RIB2 were used as parent strains; these can grow in a medium without riboflavin (RF) only if the enzyme is derepressed as the result of iron deficiency in cells. Strains growing in a medium without RF at the optimal supply of cells with iron were selected as regulatory mutants. The mutants accumulated 6,7-dimethylpterin in high concentrations and a small amount of RF in the medium and in the cells. The activity of GTP cyclohydrolase rather than that of RF synthase increased in the mutants; the activity of RF kinase and FAD pyrophosphorylase was not elevated. Hybrids produced by crossing the regulatory mutants with wild type strains did not accumulate 6,7-dimethylpterin in the medium and the activity of the GTP cyclohydrolase did not increase; this is indicative of the negative regulation for the expression of the structural gene for GTP cyclohydrolase. The authors propose a model for the regulation of GTP cyclohydrolase and RF synthase at the gene level involving iron ions as a corepressor.
提出了一种用于筛选鸟苷三磷酸环化水解酶去阻遏的季也蒙毕赤酵母突变体的阳性方法。将基因RIB2未完全阻断的突变体用作亲本菌株；只有当细胞内缺铁导致该酶去阻遏时，这些突变体才能在不含核黄素（RF）的培养基中生长。选择在细胞铁供应最佳时能在不含RF的培养基中生长的菌株作为调节突变体。这些突变体在培养基和细胞中积累了高浓度的6,7 - 二甲基蝶呤和少量的RF。突变体中鸟苷三磷酸环化水解酶的活性增加，而核黄素合酶的活性未增加；核黄素激酶和黄素腺嘌呤二核苷酸焦磷酸化酶的活性也未升高。将调节突变体与野生型菌株杂交产生的杂种在培养基中不积累6,7 - 二甲基蝶呤，鸟苷三磷酸环化水解酶的活性也不增加；这表明鸟苷三磷酸环化水解酶结构基因的表达存在负调控。作者提出了一种在基因水平上以铁离子作为辅阻遏物对鸟苷三磷酸环化水解酶和核黄素合酶进行调控的模型。
