Balcells L, Martín R, Ruiz M C, Gómez N, Ramos J, Ariño J
Dept. Bioquímica i Biologia Molecular, Facultat de Veterinària, Ed. V, Universitat Autònoma de Barcelona, Bellaterra, Spain.
FEBS Lett. 1998 Sep 18;435(2-3):241-4. doi: 10.1016/s0014-5793(98)01082-5.
We have previously shown that the mutation of the Schizosaccharomyces pombe PPZ-like protein phosphatase encoded by the gene pzh1+ results in increased tolerance to sodium and in hypersensitivity to potassium ions. A similar phenotype has also been reported for deletants in the spm1/pmk1 gene, encoding a mitogen-activated protein (MAP) kinase. We have found that the sodium tolerance phenotype of pzh1 deletants is stronger than that of spm1 mutants, and both effects are additive. Therefore, most probably both gene products mediate different pathways on sodium tolerance. In our hands, mutation of the kinase does not alter the tolerance to potassium, but it yields cells more tolerant to magnesium ions. While in budding yeast the mutations are synthetically lethal, fission yeast cells lacking both the phosphatase and the kinase genes are viable. Interestingly, their ability to export H+ to the medium is greatly impaired (although not that of pzh1 or spm1 single mutants). We have observed that, although the amount of the H+-ATPase in the plasma membrane is not altered, the activity of the enzyme is lower than normal and cannot be induced by glucose. These observations suggest that the activity of the H+-ATPase in fission yeast might be regulated by phospho-dephosphorylation mechanisms that might involve the pzh1+ and spm1+ gene products.
我们之前已经表明，由pzh1⁺基因编码的粟酒裂殖酵母PPZ样蛋白磷酸酶发生突变会导致对钠离子的耐受性增加以及对钾离子的超敏反应。对于编码丝裂原活化蛋白（MAP）激酶的spm1/pmk1基因的缺失突变体，也报道了类似的表型。我们发现，pzh1缺失突变体的耐钠表型比spm1突变体更强，且两种效应是相加的。因此，很可能这两种基因产物在耐钠性方面介导不同的途径。在我们的研究中，激酶的突变不会改变对钾离子的耐受性，但会使细胞对镁离子更耐受。在芽殖酵母中，这些突变是合成致死的，而缺乏磷酸酶和激酶基因的裂殖酵母细胞是可存活的。有趣的是，它们向培养基中输出H⁺的能力大大受损（尽管pzh1或spm1单突变体并非如此）。我们观察到，尽管质膜中H⁺-ATP酶的量没有改变，但其酶活性低于正常水平，且不能被葡萄糖诱导。这些观察结果表明，裂殖酵母中H⁺-ATP酶的活性可能受磷酸化-去磷酸化机制调控，该机制可能涉及pzh1⁺和spm1⁺基因产物。
