Campa M J, Farrell F X, Lapetina E G, Chang K J
Division of Cell Biology, Burroughs Wellcome Co., Research Triangle Park, NC 27709.
Biochem J. 1993 May 15;292 ( Pt 1)(Pt 1):231-6. doi: 10.1042/bj2920231.
Rap2B, a member of the ras superfamily of low-molecular-mass GTP-binding proteins, induced a characteristic rearrangement of the pigment granules in Xenopus oocytes following its microinjection, resulting in numerous unpigmented spots on the animal hemisphere. This phenomenon, termed 'mottling', was also induced by microinjection of in vitro-transcribed Rap2B RNA or of purified recombinant Rap2A. Following the microinjection of Rap2B, more than 90% of the oocytes showed signs of mottling within 10 h. The time course of mottling paralleled the association of the recombinant Rap2B with an oocyte membrane fraction. Like other members of the ras superfamily, Rap2B possesses a C-terminal CAAX motif that serves as a signal for post-translational processing. Mutation of the cysteine residue in the CAAX motif to serine prevents the association of Rap2B with oocyte membranes, and also prevents mottling. This result suggests that post-translational processing of Rap2B is required for the observed effect. Mottling was blocked by boiling Rap2B prior to its microinjection or by co-injection of the cytoskeletal reagent phalloidin.
Rap2B是低分子量GTP结合蛋白ras超家族的成员之一，在显微注射到非洲爪蟾卵母细胞后，可诱导色素颗粒发生特征性重排，导致动物半球出现大量无色素斑点。这种现象被称为“斑驳化”，显微注射体外转录的Rap2B RNA或纯化的重组Rap2A也可诱导该现象。显微注射Rap2B后，超过90%的卵母细胞在10小时内出现斑驳化迹象。斑驳化的时间进程与重组Rap2B与卵母细胞膜组分的结合情况平行。与ras超家族的其他成员一样，Rap2B具有C端CAAX基序，该基序作为翻译后加工的信号。将CAAX基序中的半胱氨酸残基突变为丝氨酸可阻止Rap2B与卵母细胞膜的结合，也可阻止斑驳化。该结果表明，Rap2B的翻译后加工是观察到的效应所必需的。在显微注射前将Rap2B煮沸或共注射细胞骨架试剂鬼笔环肽可阻止斑驳化。
