Meijer A H, de Kam R J, d'Erfurth I, Shen W, Hoge J H
Institute of Molecular Plant Sciences, Leiden University, Clusius Laboratory, The Netherlands.
Mol Gen Genet. 2000 Feb;263(1):12-21. doi: 10.1007/pl00008671.
Proteins of the closely related homeodomain-leucine zipper (HD-Zip) families I and II in plants are putative transcription factors that interact with similar pseudopalindromic DNA recognition sites. We have previously described the Oshox1 gene from rice, which encodes an HD-Zip II protein. To identify further rice HD-Zip proteins, one-hybrid screens were performed in yeast strains containing a HIS3 reporter gene with upstream HD-Zip recognition sites. This resulted in the isolation of six new cDNAs encoding HD-Zip proteins belonging to family I (Oshox4, -5, -6) or family II (Oshox2, -3, -7). In transient assays, using rice suspension-cultured cells transformed by particle bombardment, we showed previously that Oshox1 can transcriptionally repress the activity of reporter gene constructs with upstream HD-Zip binding sites. Here, we confirm the repression properties of Oshox1 by showing that the repression function can be conferred on a heterologous DNA-binding domain. This portable functional domain (residues 1-155) is located proximal to the HD-Zip domain. In yeast, the same region of the Oshox1 protein was found to confer transcriptional activation instead of repression, pointing to the possibility that cell type-specific factors may determine the functional properties of the Oshox1 protein in rice. Like Oshox1, another HD-Zip family II protein (Oshox3) was also found to function as a transcriptional repressor in rice cells. In contrast, two HD-Zip I family proteins (Oshox4 and -5) appeared to act as activators in both rice and yeast cells. Results of two-hybrid assays and electrophoretic mobility shift assays strongly suggest that all HD-Zip proteins of families I and II can form homodimers and also heterodimers with all HD-Zip proteins of the same family. Heterodimerization across the HD-Zip families I and II apparently does not to occur.
植物中密切相关的同源异型域-亮氨酸拉链（HD-Zip）I 族和 II 族蛋白是假定的转录因子，它们与相似的假回文 DNA 识别位点相互作用。我们之前描述过水稻中的 Oshox1 基因，它编码一种 HD-Zip II 蛋白。为了进一步鉴定水稻 HD-Zip 蛋白，我们在含有带有上游 HD-Zip 识别位点的 HIS3 报告基因的酵母菌株中进行了单杂交筛选。这导致分离出六个新的 cDNA，它们编码属于 I 族（Oshox4、-5、-6）或 II 族（Oshox2、-3、-7）的 HD-Zip 蛋白。在瞬时分析中，利用通过粒子轰击转化的水稻悬浮培养细胞，我们之前表明 Oshox1 可以转录抑制具有上游 HD-Zip 结合位点的报告基因构建体的活性。在这里，我们通过表明抑制功能可以赋予异源 DNA 结合结构域来证实 Oshox1 的抑制特性。这个可移植的功能结构域（第 1 - 155 位氨基酸残基）位于 HD-Zip 结构域附近。在酵母中，发现 Oshox1 蛋白的相同区域赋予转录激活而非抑制作用，这表明细胞类型特异性因子可能决定 Oshox1 蛋白在水稻中的功能特性。与 Oshox1 一样，另一种 HD-Zip II 族蛋白（Oshox3）在水稻细胞中也被发现作为转录抑制因子发挥作用。相比之下，两种 HD-Zip I 族蛋白（Oshox4 和 -5）在水稻和酵母细胞中似乎都作为激活因子起作用。双杂交分析和电泳迁移率变动分析的结果强烈表明，I 族和 II 族的所有 HD-Zip 蛋白都可以形成同二聚体，也可以与同一家族的所有 HD-Zip 蛋白形成异二聚体。HD-Zip I 族和 II 族之间显然不会发生异源二聚化。
