McCammon M T, Hartmann M A, Bottema C D, Parks L W
J Bacteriol. 1984 Feb;157(2):475-83. doi: 10.1128/jb.157.2.475-483.1984.
Various nystatin-resistant mutants defective in S-adenosylmethionine: delta 24-sterol-C-methyltransferase (EC 2.1.1.41) were shown to possess alleles of the same gene, erg6. The genetic map location of erg6 was shown to be close to trp1 on chromosome 4. Despite the single locus for erg6, S-adenosylmethionine: delta 24-sterol-C-methyltransferase enzyme activity was found in three separate fractions: mitochondria, microsomes, and the "floating lipid layer." The amount of activity in each fraction could be manipulated by assay conditions. The lipids and lipid synthesis of mutants of Saccharomyces cerevisiae defective in the delta 24-sterol-C-methyltransferase were compared with a C5(6) desaturase mutant and parental wild types. No ergosterol (C28 sterol) could be detected in whole-cell sterol extracts of the erg6 mutants, the limits of detection being less than 10(-11) mol of ergosterol per 10(8) cells. The distribution of accumulated sterols by these mutants varied with growth phase and between free and esterified fractions. The steryl ester concentrations of the mutants were eight times higher than those of the wild type from exponential growth samples. However, the concentration of the ester accumulated by the mutants was not as great in stationary-phase cells. Whereas the head group phospholipid composition was the same between parental and mutant strains, strain-dependent changes in fatty acids were observed, most notably a 40% increase in the oleic acid content of phosphatidylethanolamine of one erg6 mutant, JR5.
多种对制霉菌素耐药的突变体在S-腺苷甲硫氨酸：δ24-甾醇-C-甲基转移酶（EC 2.1.1.41）方面存在缺陷，结果表明它们拥有同一基因erg6的等位基因。erg6的遗传图谱定位显示在4号染色体上靠近trp1。尽管erg6只有一个基因座，但在三个不同的组分中发现了S-腺苷甲硫氨酸：δ24-甾醇-C-甲基转移酶的酶活性，这三个组分分别是线粒体、微粒体和“漂浮脂质层”。每个组分中的活性量可通过测定条件进行调控。将酿酒酵母中δ24-甾醇-C-甲基转移酶缺陷的突变体的脂质及脂质合成与一个C5(6)去饱和酶突变体及亲本野生型进行了比较。在erg6突变体的全细胞甾醇提取物中未检测到麦角固醇（C28甾醇），检测限为每10(8)个细胞中麦角固醇含量低于10(-11)摩尔。这些突变体积累的甾醇分布随生长阶段以及游离和酯化组分的不同而变化。来自指数生长期样品的突变体的甾醇酯浓度比野生型高八倍。然而，在稳定期细胞中，突变体积累的酯浓度没有那么高。虽然亲本菌株和突变体菌株之间的头部基团磷脂组成相同，但观察到脂肪酸存在菌株依赖性变化，最显著的是一个erg6突变体JR5的磷脂酰乙醇胺的油酸含量增加了40%。
