Wu J, Tolstykh T, Lee J, Boyd K, Stock J B, Broach J R
Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
EMBO J. 2000 Nov 1;19(21):5672-81. doi: 10.1093/emboj/19.21.5672.
The phosphoprotein phosphatase 2A (PP2A) catalytic subunit contains a methyl ester on its C-terminus, which in mammalian cells is added by a specific carboxyl methyltransferase and removed by a specific carboxyl methylesterase. We have identified genes in yeast that show significant homology to human carboxyl methyltransferase and methylesterase. Extracts of wild-type yeast cells contain carboxyl methyltransferase activity, while extracts of strains deleted for one of the methyltransferase genes, PPM1, lack all activity. Mutation of PPM1 partially disrupts the PP2A holoenzyme in vivo and ppm1 mutations exhibit synthetic lethality with mutations in genes encoding the B or B' regulatory subunit. Inactivation of PPM1 or overexpression of PPE1, the yeast gene homologous to bovine methylesterase, yields phenotypes similar to those observed after inactivation of either regulatory subunit. These phenotypes can be reversed by overexpression of the B regulatory subunit. These results demonstrate that Ppm1 is the sole PP2A methyltransferase in yeast and that its activity is required for the integrity of the PP2A holoenzyme.
磷酸蛋白磷酸酶2A（PP2A）催化亚基在其C末端含有一个甲酯，在哺乳动物细胞中，该甲酯由特定的羧基甲基转移酶添加，并由特定的羧基甲酯酶去除。我们在酵母中鉴定出了与人类羧基甲基转移酶和甲酯酶具有显著同源性的基因。野生型酵母细胞提取物含有羧基甲基转移酶活性，而缺失甲基转移酶基因之一PPM1的菌株提取物则完全没有活性。PPM1的突变在体内部分破坏了PP2A全酶，并且ppm1突变与编码B或B'调节亚基的基因突变表现出合成致死性。PPM1的失活或与牛甲酯酶同源的酵母基因PPE1的过表达产生的表型与任一调节亚基失活后观察到的表型相似。这些表型可以通过B调节亚基的过表达来逆转。这些结果表明，Ppm1是酵母中唯一的PP2A甲基转移酶，其活性是PP2A全酶完整性所必需的。
