Miller M, Reddy B A, Kloc M, Li X X, Dreyer C, Etkin L D
Department of Molecular Genetics, University of Texas M.D. Anderson Cancer Center, Houston 77030.
Development. 1991 Oct;113(2):569-75. doi: 10.1242/dev.113.2.569.
We describe the characterization in Xenopus laevis of a nuclear protein, xnf7, which is first detected in the oocyte GV and is eventually enriched in nuclei of cells of the adult brain. Previous studies have shown that this protein contains zinc-finger-like structures and acidic domains typical of transcriptional activators, and is phosphorylated in vitro by p34cdc2 protein kinase. The protein also binds to double-stranded DNA. These data suggest that xnf7 may function as a transcription factor. During oocyte maturation, xnf7 is released into the cytoplasm and is not detectable in nuclei until the mid-blastula-gastrula stage of development. Western blot analysis of xnf7 isolated from oocytes and eggs showed the existence of multiple bands or isoforms of the protein. Unique isoforms that are generated during oocyte maturation are the result of phosphorylation. The phosphorylated isoforms remain in the cytoplasm until the mid-blastula stage. The re-accumulation of protein in the embryonic nuclei at this time correlates with the increase in abundance of the less phosphorylated isoforms. The xnf7 protein possesses a nuclear localization signal (NLS) similar to the bipartite signal found in nucleoplasmin. Newly synthesized xnf7 accumulated in the oocyte GV to detectable levels within a few hours following synthesis suggesting that retention of the protein in the cytoplasm during early cleavage may be due to a process that interferes with the function of the NLS. These data suggest that compartmentalization and/or post-translational modification of the nuclear protein xnf7 may be involved in regulating its function during early development.
我们描述了非洲爪蟾中一种核蛋白xnf7的特性，该蛋白最初在卵母细胞生发泡中被检测到，最终在成年大脑细胞的细胞核中富集。先前的研究表明，这种蛋白含有锌指样结构和转录激活因子典型的酸性结构域，并且在体外可被p34cdc2蛋白激酶磷酸化。该蛋白还能与双链DNA结合。这些数据表明xnf7可能作为一种转录因子发挥作用。在卵母细胞成熟过程中，xnf7释放到细胞质中，直到发育的囊胚中期 - 原肠胚阶段才能在细胞核中检测到。对从卵母细胞和卵中分离出的xnf7进行蛋白质免疫印迹分析表明，该蛋白存在多条条带或异构体。在卵母细胞成熟过程中产生的独特异构体是磷酸化的结果。磷酸化的异构体一直留在细胞质中，直到囊胚中期。此时胚胎细胞核中蛋白质的重新积累与磷酸化程度较低的异构体丰度增加相关。xnf7蛋白拥有一个类似于核质蛋白中发现的双分型信号的核定位信号（NLS）。新合成的xnf7在合成后几小时内就在卵母细胞生发泡中积累到可检测水平，这表明在早期卵裂过程中该蛋白保留在细胞质中可能是由于一个干扰NLS功能的过程。这些数据表明，核蛋白xnf7的区室化和/或翻译后修饰可能参与早期发育过程中对其功能的调节。
