Cohen A, Perzov N, Nelson H, Nelson N
Department of Biochemistry, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
J Biol Chem. 1999 Sep 17;274(38):26885-93. doi: 10.1074/jbc.274.38.26885.
Null mutations in genes encoding V-ATPase subunits in Saccharomyces cerevisiae result in a phenotype that is unable to grow at high pH and is sensitive to high and low metal-ion concentrations. Treatment of these null mutants with ethylmethanesulfonate causes mutations that suppress the V-ATPase null phenotype, and the mutant cells are able to grow at pH 7.5. The suppressor mutants were denoted as svf (suppressor of V-ATPase function). The frequency of svf is relatively high, suggesting a large target containing several genes for the ethylmethanesulfonate mutagenesis. The suppressors' frequency is dependent on the individual genes that were inactivated to manifest the V-ATPase null mutation. The svf mutations are recessive, because crossing the svf mutants with their corresponding V-ATPase null mutants resulted in diploid strains that are unable to grow at pH 7.5. A novel gene family in which null mutations cause pleiotropic effects on metal-ion resistance or sensitivity and distribution of membrane proteins in different targets was discovered. The family was defined as VTC (Vacuolar Transporter Chaperon) and it contains four genes in the S. cerevisiae genome. Inactivation of one of them, VTC1, in the background of V-ATPase null mutations resulted in svf phenotype manifested by growth at pH 7.5. Deletion of the VTC1 gene (DeltaVTC1) results in a reduced amount of V-ATPase in the vacuolar membrane. These mutant cells fail to accumulate quinacrine into their vacuoles, but they are able to grow at pH 7.5. The VTC1 null mutant also results in a reduced amount of the plasma membrane H(+)-ATPase (Pma1p) in membrane preparations and possibly mis-targeting. This observation may provide an explanation for the svf phenotype in the double disruptant mutants of DeltaVTC1 and DeltaVMA subunits.
酿酒酵母中编码V - ATP酶亚基的基因发生无效突变，会导致一种表型，即无法在高pH值下生长，且对高浓度和低浓度金属离子敏感。用甲磺酸乙酯处理这些无效突变体可导致抑制V - ATP酶无效表型的突变，突变细胞能够在pH 7.5下生长。这些抑制突变体被命名为svf（V - ATP酶功能的抑制子）。svf的频率相对较高，表明甲磺酸乙酯诱变存在一个包含多个基因的大靶点。抑制子的频率取决于为表现V - ATP酶无效突变而被灭活的单个基因。svf突变是隐性的，因为将svf突变体与其相应的V - ATP酶无效突变体杂交会产生无法在pH 7.5下生长的二倍体菌株。发现了一个新的基因家族，其中的无效突变会对金属离子抗性或敏感性以及膜蛋白在不同靶点中的分布产生多效性影响。该家族被定义为VTC（液泡转运伴侣），在酿酒酵母基因组中包含四个基因。在V - ATP酶无效突变的背景下，其中一个基因VTC1的失活导致了在pH 7.5下生长所表现出的svf表型。VTC1基因的缺失（ΔVTC1）导致液泡膜中V - ATP酶的量减少。这些突变细胞无法将喹吖因积累到液泡中，但它们能够在pH 7.5下生长。VTC1无效突变体还导致膜制剂中质膜H⁺ - ATP酶（Pma1p）的量减少，并且可能存在错误靶向。这一观察结果可能为ΔVTC1和ΔVMA亚基的双破坏突变体中的svf表型提供一种解释。
