McGonigle B, Bouhidel K, Irish V F
Department of Biology, Osborn Memorial Laboratories, Yale University, New Haven, Connecticut 06520-8104, USA.
Genes Dev. 1996 Jul 15;10(14):1812-21. doi: 10.1101/gad.10.14.1812.
The Arabidopsis APETALA3 (AP3) and PISTILLATA (PI) proteins are thought to act as transcription factors and are required for specifying floral organ identities. To define the nuclear localization signals within these proteins, we generated translational fusions of the coding regions of AP3 and PI to the bacterial uidA gene that encodes beta-glucuronidase (GUS). Transient transformation assays of either the AP3-GUS or PI-GUS fusion protein alone resulted in cytoplasmic localization of GUS activity. However, coexpression of AP3-GUS with PI, or PI-GUS with AP3, resulted in nuclear localization of GUS activity. Stable transformation with these fusion proteins in Arabidopsis showed similar results. The nuclear colocalization signals in AP3 and PI were mapped to the amino-terminal regions of each protein. These observations suggest that the interaction of the AP3 and PI gene products results in the formation of a protein complex that generates or exposes a colocalization signal required to translocate the resulting complex into the nucleus. The colocalization phenomenon that we have described represents a novel mechanism to coordinate the functions of transcription factors within the nucleus.
拟南芥的APETALA3（AP3）蛋白和PISTILLATA（PI）蛋白被认为作为转录因子发挥作用，并且是决定花器官特征所必需的。为了确定这些蛋白中的核定位信号，我们构建了AP3和PI编码区与编码β-葡萄糖醛酸酶（GUS）的细菌uidA基因的翻译融合体。单独对AP3-GUS或PI-GUS融合蛋白进行瞬时转化分析，结果显示GUS活性定位于细胞质中。然而，AP3-GUS与PI共表达，或PI-GUS与AP3共表达，结果显示GUS活性定位于细胞核中。用这些融合蛋白在拟南芥中进行稳定转化也得到了类似的结果。AP3和PI中的核共定位信号被定位到每个蛋白的氨基末端区域。这些观察结果表明，AP3和PI基因产物的相互作用导致形成一种蛋白复合物，该复合物产生或暴露一种将所得复合物转运到细胞核中所需的共定位信号。我们所描述的共定位现象代表了一种协调细胞核内转录因子功能的新机制。
