King M W, Roberts J M, Eisenman R N
Mol Cell Biol. 1986 Dec;6(12):4499-508. doi: 10.1128/mcb.6.12.4499-4508.1986.
We isolated and characterized Xenopus laevis c-myc cDNAs from an oocyte-specific library. These cDNA clones encompass 2.35 kilobases of the X. laevis c-myc RNA and contain the entire coding domain of 1,257 nucleotides of the 419-amino acid-long X. laevis c-myc protein. The 2.7-kilobase X. laevis c-myc mRNA is expressed in the oocyte, maintained in the egg, and is present throughout the early cleavage stages of embryogenesis. At the time of transcriptional activation in the embryo the c-myc RNA levels show a significant decline and then reaccumulate continuously throughout the remainder of premorphogenic development. At the early neurula stage of embryogenesis the pattern of c-myc RNA expression is elevated in the mesoderm with respect to the endoderm and ectoderm. In the adult X. laevis the c-myc mRNA is expressed in some (e.g., skin, muscle) but not all differentiated tissues. The X. laevis c-myc protein migrates as a doublet of 61,000- and 64,000-dalton species. Both species are phosphorylated in oocytes and somatic cells, exhibit extremely short half-lives of less than 30 min, and are localized to the nuclear fraction of somatic cells. By contrast, the oocyte protein shows both cytoplasmic and germinal vesicle distribution and appears to be stable.
我们从一个卵母细胞特异性文库中分离并鉴定了非洲爪蟾的c-myc cDNA。这些cDNA克隆包含2.35千碱基的非洲爪蟾c-myc RNA，并且含有编码419个氨基酸长的非洲爪蟾c-myc蛋白的1257个核苷酸的完整编码结构域。2.7千碱基的非洲爪蟾c-myc mRNA在卵母细胞中表达，在卵中得以维持，并在胚胎发育的早期卵裂阶段全程存在。在胚胎中转录激活时，c-myc RNA水平显著下降，然后在形态发生前发育的剩余阶段持续重新积累。在胚胎发育的早期神经胚阶段，c-myc RNA的表达模式在中胚层相对于内胚层和外胚层有所升高。在成年非洲爪蟾中，c-myc mRNA在一些（如皮肤、肌肉）但并非所有分化组织中表达。非洲爪蟾c-myc蛋白以61,000道尔顿和64,000道尔顿两种形式迁移。这两种形式在卵母细胞和体细胞中均被磷酸化，半衰期极短，不到30分钟，并且定位于体细胞的细胞核部分。相比之下，卵母细胞蛋白在细胞质和生发泡中均有分布，并且似乎是稳定的。
