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首页> 外文期刊>Molecular and Cellular Biology >Characterization of tobacco protein kinase NPK5, a homolog of Saccharomyces cerevisiae SNF1 that constitutively activates expression of the glucose-repressible SUC2 gene for a secreted invertase of S. cerevisiae.
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Characterization of tobacco protein kinase NPK5, a homolog of Saccharomyces cerevisiae SNF1 that constitutively activates expression of the glucose-repressible SUC2 gene for a secreted invertase of S. cerevisiae.

机译：烟草蛋白激酶NPK5（啤酒酵母SNF1的同系物）的特征，该酶可组成性地激活酿酒酵母分泌型转化酶的葡萄糖可抑制SUC2基因的表达。

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We have isolated a cDNA (cNPK5) that encodes a protein kinase of 511 amino acids from suspension cultures of tobacco cells. The predicted kinase domain of NPK5 is 65% identical in terms of amino acid sequence to that of the SNF1 serine/threonine protein kinase of Saccharomyces cerevisiae, which plays a central role in catabolite repression in yeast cells. SNF1 positively regulates transcription of various glucose-repressible genes of the yeast, such as the SUC2 gene for a secreted invertase, in response to glucose deprivation: snf1 mutants cannot utilize sucrose as a carbon source. Expression of cNPK5 in yeast cells allowed the snf1 mutant cells to utilize sucrose for growth and caused constitutive expression of the SUC2 gene in wild-type cells even in the presence of glucose, an indication that the NPK5 protein is present in a constitutively active form in S. cerevisiae. On the other hand, expression of cNPK5 failed to suppress the growth defect of the snf4 mutant cells in the presence of sucrose and to induce expression of the SUC2 gene. These results indicate that SNF4 is required for the induction of SUC2 expression by NPK5, as by SNF1, even if NPK5 is constitutively active in S. cerevisiae. The recombinant NPK5 protein is capable of autophosphorylation in vitro in a reaction that requires Mn2+ rather than Mg2+ ions but is inhibited by Ca2+ ions. Both dicotyledonous and monocotyledonous plants have several copies of the NPK5-related gene, which probably constitute a small gene family. NPK5-related genes were found to be expressed in the roots, leaves, and stems of tobacco plants. The high degree of structural conservation and the functional similarity of NPK5 to SNF1 lead us to speculate that NPK5 (or a related kinase) also plays a role in sugar metabolism in higher plants.
机译：我们已经从烟草细胞的悬浮培养物中分离出一个编码511个氨基酸的蛋白激酶的cDNA（cNPK5）。就氨基酸序列而言，NPK5的预测激酶结构域与酿酒酵母的SNF1丝氨酸/苏氨酸蛋白激酶的氨基酸序列具有65％的同一性，在酵母细胞中分解代谢物的阻遏中起着核心作用。 SNF1积极调节酵母的各种葡萄糖可抑制基因的转录，例如分泌型转化酶的SUC2基因，以响应葡萄糖剥夺：snf1突变体无法利用蔗糖作为碳源。酵母细胞中cNPK5的表达使snf1突变细胞能够利用蔗糖生长，甚至在葡萄糖存在的情况下，也能在野生型细胞中引起SUC2基因的组成型表达，这表明NPK5蛋白以组成型活性形式存在于葡萄糖中。酿酒酵母。另一方面，在蔗糖存在下，cNPK5的表达不能抑制snf4突变细胞的生长缺陷并不能诱导SUC2基因的表达。这些结果表明，即使NPK5在酿酒酵母中具有组成性活性，SNP4也需要像SNF1一样被NPK5诱导SUC2表达。在需要Mn2 +而不是Mg2 +离子但受Ca2 +离子抑制的反应中，重组NPK5蛋白能够在体外自磷酸化。双子叶植物和单子叶植物都具有NPK5相关基因的几个拷贝，这可能构成一个小的基因家族。发现与NPK5相关的基因在烟草植物的根，叶和茎中表达。 NPK5与SNF1的高度结构保守性和功能相似性使我们推测NPK5（或相关激酶）在高等植物的糖代谢中也起作用。

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