Van Hoof C, Janssens V, De Baere I, de Winde J H, Winderickx J, Dumortier F, Thevelein J M, Merlevede W, Goris J
Afdeling Biochemie, Faculteit Geneeskunde, Katholieke Universiteit Leuven, Herestraat 49, Leuven, B-3000, Belgium.
J Mol Biol. 2000 Sep 8;302(1):103-20. doi: 10.1006/jmbi.2000.4062.
The Saccharomyces cerevisiae gene YPA1 encodes a protein homologous to the phosphotyrosyl phosphatase activator, PTPA, of the mammalian protein phosphatase type 2A (PP2A). In order to examine the biological role of PTPA, we disrupted YPA1 and characterised the phenotype of the ypa1Delta mutant. Comparison of the growth rate of the wild-type strain and the ypa1Delta mutant on glucose-rich medium after nutrient depletion showed that the ypa1Delta mutant traversed the lag period more rapidly. This accelerated progression through "Start" was also observed after release from alpha-factor-induced G1 arrest as evidenced by a higher number of budding cells, a faster increase in CLN2 mRNA expression and a more rapid reactivation of Cdc28 kinase activity. This phenotype was specific for deletion of YPA1 since it was not observed when YPA2, the second PTPA gene in budding yeast was deleted. Reintroduction of YPA1 or the human PTPA cDNA in the ypa1Delta mutant suppressed this phenotype as opposed to overexpression of YPA2. Disruption of both YPA genes is lethal, since sporulation of heterozygous diploids resulted in at most three viable spores, none of them with a ypa1Delta ypa2Delta genotype. This observation indicates that YPA1 and YPA2 share some essential functions. We compared the ypa1Delta mutant phenotype with a PP2A double deletion mutant and a PP2A temperature-sensitive mutant. The PP2A-deficient yeast strain also showed accelerated progression through the G1 phase. In addition, both PP2A and ypa1Delta mutants show similar aberrant bud morphology. This would support the notion that YPA1 may act as a positive regulator of PP2A in vivo.
酿酒酵母基因YPA1编码一种与哺乳动物2A型蛋白磷酸酶（PP2A）的磷酸酪氨酸磷酸酶激活剂PTPA同源的蛋白质。为了研究PTPA的生物学作用，我们破坏了YPA1并对ypa1Delta突变体的表型进行了表征。营养耗尽后，在富含葡萄糖的培养基上比较野生型菌株和ypa1Delta突变体的生长速率，结果表明ypa1Delta突变体更快地度过了延迟期。从α因子诱导的G1期阻滞释放后，也观察到通过“起始点”的这种加速进程，这表现为出芽细胞数量更多、CLN2 mRNA表达更快增加以及Cdc28激酶活性更快重新激活。这种表型是YPA1缺失所特有的，因为当删除芽殖酵母中的第二个PTPA基因YPA2时未观察到这种表型。与YPA2的过表达相反，在ypa1Delta突变体中重新引入YPA1或人PTPA cDNA可抑制这种表型。两个YPA基因的破坏是致死的，因为杂合二倍体的孢子形成最多产生三个活孢子，其中没有一个具有ypa1Delta ypa2Delta基因型。这一观察结果表明YPA1和YPA2具有一些基本功能。我们将ypa1Delta突变体表型与PP2A双缺失突变体和PP2A温度敏感突变体进行了比较。PP2A缺陷型酵母菌株也显示出通过G1期的加速进程。此外，PP2A和ypa1Delta突变体都表现出相似的异常芽形态。这支持了YPA1可能在体内作为PP2A的正调节因子的观点。
