Nelson H, Nelson N
Roche Institute of Molecular Biology, Roche Research Center, Nutley, NJ 07110.
Proc Natl Acad Sci U S A. 1990 May;87(9):3503-7. doi: 10.1073/pnas.87.9.3503.
The main function of vacuolar H(+)-ATPases in eukaryotic cells is to generate proton and electrochemical gradients across the membranes of the vacuolar system. The enzyme is composed of a catalytic sector with five subunits (A-E) and a membrane sector containing at least two subunits (a and c). We disrupted two genes of this enzyme, in yeast cells, one encoding a subunit of the membrane sector (subunit c) and another encoding a subunit of the catalytic sector (subunit B). The resulting mutants did not grow in medium with a pH value higher than 6.5 and grew well only within a narrow pH range around 5.5. Transformation of the mutants with plasmids containing the corresponding genes repaired the mutations. Thus failure to lower the pH in the vacuolar system of yeast, and probably other eukaryotic cells, is lethal and the mutants may survive only if a low external pH allows for this acidification by fluid-phase endocytosis.
液泡H(+) -ATP酶在真核细胞中的主要功能是在液泡系统的膜上产生质子和电化学梯度。该酶由一个含有五个亚基（A - E）的催化部分和一个至少含有两个亚基（a和c）的膜部分组成。我们在酵母细胞中破坏了该酶的两个基因，一个编码膜部分的亚基（亚基c），另一个编码催化部分的亚基（亚基B）。产生的突变体在pH值高于6.5的培养基中不能生长，仅在5.5左右的狭窄pH范围内生长良好。用含有相应基因的质粒转化突变体可修复突变。因此，酵母以及可能其他真核细胞的液泡系统中未能降低pH值是致命的，并且只有当低外部pH值允许通过液相内吞作用进行这种酸化时，突变体才可能存活。
