Kitten G T, Nigg E A
Swiss Institute for Experimental Cancer Research (ISREC), Epalinges.
J Cell Biol. 1991 Apr;113(1):13-23. doi: 10.1083/jcb.113.1.13.
Recent evidence suggests that the conserved COOH-terminal CaaX motif of nuclear lamins may play a role in targeting newly synthesized proteins to the nuclear envelope. We have shown previously that in rabbit reticulocyte lysates the cysteine residue of the CaaX motif of chicken lamin B2 is necessary for incorporation of a derivative of mevalonic acid, the precursor of isoprenoids. Here we have analyzed the properties of normal and mutated forms of chicken lamin B2 stably expressed in mouse L cells. Mutation of the cysteine residue of the CaaX motif to alanine or introduction of a stop codon immediately after the cysteine residue was found to abolish both isoprenylation and carboxyl methylation of transfected lamin B2. Concomitantly, although nuclear import of the mutant lamin B2 proteins was preserved, their association with the inner nuclear membrane was severely impaired. From these results we conclude that the COOH-terminal CaaX motif is required for isoprenylation and carboxyl methylation of lamins in vivo, and that these modifications are important for association of B-type lamins with the nucleoplasmic surface of the inner nuclear membrane.
最近的证据表明，核纤层蛋白保守的COOH末端CaaX基序可能在将新合成的蛋白质靶向核膜中发挥作用。我们之前已经表明，在兔网织红细胞裂解物中，鸡层粘连蛋白B2的CaaX基序的半胱氨酸残基对于类异戊二烯前体甲羟戊酸衍生物的掺入是必需的。在这里，我们分析了在小鼠L细胞中稳定表达的正常和突变形式的鸡层粘连蛋白B2的特性。发现将CaaX基序的半胱氨酸残基突变为丙氨酸或在半胱氨酸残基后立即引入终止密码子会消除转染的层粘连蛋白B2的异戊二烯化和羧基甲基化。同时，尽管突变的层粘连蛋白B2蛋白的核输入得以保留，但其与内核膜的结合却严重受损。从这些结果我们得出结论，COOH末端CaaX基序是体内核纤层蛋白异戊二烯化和羧基甲基化所必需的，并且这些修饰对于B型核纤层蛋白与内核膜核质表面的结合很重要。
