Li X, Shou W, Kloc M, Reddy B A, Etkin L D
Department of Molecular Genetics, University of Texas M.D. Anderson Cancer Center, Houston 77030.
Exp Cell Res. 1994 Aug;213(2):473-81. doi: 10.1006/excr.1994.1225.
The function of proteins is often regulated by their association with specific subcellular structures. Xenopus nuclear factor 7 (xnf7) is a putative transcription factor that is selectively retained in the cytoplasm from fertilization through the mid blastula transition (MBT). Cytoplasmic retention is dependent upon the presence of a 22-amino-acid cytoplasmic retention domain and the phosphorylation of two sites (site 1 and site 2) within the protein. We show that the N-terminal acidic domain of xnf7 transactivated a reporter gene in transfected cells, supporting its function as a transcription factor. During mitosis xnf7 was associated with the mitotic spindle and chromosomes, while during the short embryonic interphase it was associated with structures at the poles which were most likely centrosomes. The association with these structures was dependent upon the presence of protein domains and the phosphorylation of a specific phosphorylation site (site 2). In addition, we determined that association with the spindle or centrosomes was not necessary for cytoplasmic retention prior to the MBT. We suggest that the association of xnf7 with these structures is due to its interaction with other proteins that are colocalized.
蛋白质的功能通常受其与特定亚细胞结构的结合所调控。非洲爪蟾核因子7（xnf7）是一种假定的转录因子，从受精到囊胚中期转换（MBT）期间，它被选择性地保留在细胞质中。细胞质保留依赖于一个22个氨基酸的细胞质保留结构域的存在以及该蛋白质内两个位点（位点1和位点2）的磷酸化。我们发现，xnf7的N端酸性结构域在转染细胞中可激活报告基因，这支持了它作为转录因子的功能。在有丝分裂期间，xnf7与有丝分裂纺锤体和染色体相关联，而在短暂的胚胎间期，它与极区的结构相关联，这些结构很可能是中心体。与这些结构的关联依赖于蛋白质结构域的存在以及一个特定磷酸化位点（位点2）的磷酸化。此外，我们确定在MBT之前，与纺锤体或中心体的关联对于细胞质保留并非必需。我们认为，xnf7与这些结构的关联是由于它与共定位的其他蛋白质相互作用所致。
