Sridhar Vaniyambadi V, Surendrarao Anandkumar, Gonzalez Deyarina, Conlan R Steven, Liu Zhongchi
Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA.
Proc Natl Acad Sci U S A. 2004 Aug 3;101(31):11494-9. doi: 10.1073/pnas.0403055101. Epub 2004 Jul 26.
Transcription repression plays important roles in preventing crucial regulatory proteins from being expressed in inappropriate temporal or spatial domains. LEUNIG (LUG) and SEUSS (SEU) normally act to prevent ectopic expression of the floral homeotic gene AGAMOUS in flowers. LUG encodes a protein with sequence similarities to the yeast Tup1 corepressor. SEU encodes a plant-specific regulatory protein with sequence similarity in a conserved dimerization domain to the LIM-domain binding 1/Chip proteins in mouse and Drosophila. Despite the molecular isolation of LUG and SEU, the biochemical function of these two proteins remains uncharacterized, and the mechanism of AGAMOUS repression remains unknown. Here, we report that LUG and SEU interact directly in vitro and in vivo. Furthermore, LUG exhibits a strong repressor activity on several heterologous promoters in yeast and plant cells. SEU, in contrast, does not exhibit any direct repressor activity, but can repress reporter gene expression only in the presence of LUG, indicating a possible role of SEU as an adaptor protein for LUG. Our results demonstrate that LUG encodes a functional homologue of Tup1 and that SEU may function similarly to Ssn6, an adaptor protein of Tup1. We have defined the LUG/LUH, Flo8, single-strand DNA-binding protein domain of LUG as both necessary and sufficient for the interaction with SEU and two domains of LUG as important for its repressor function. Our work provides functional insights into plant transcriptional corepressors and reveals both conservation and distinctions between plant corepressors and those of yeast and animals.
转录抑制在防止关键调节蛋白在不适当的时间或空间域中表达方面发挥着重要作用。LEUNIG（LUG）和SEUSS（SEU）通常起到防止花同源异型基因AGAMOUS在花中异位表达的作用。LUG编码一种与酵母Tup1共抑制因子具有序列相似性的蛋白质。SEU编码一种植物特异性调节蛋白，其在保守的二聚化结构域中的序列与小鼠和果蝇中的LIM结构域结合1/Chip蛋白相似。尽管LUG和SEU已在分子水平上被分离，但这两种蛋白质的生化功能仍未得到表征，AGAMOUS抑制的机制也仍然未知。在这里，我们报告LUG和SEU在体外和体内直接相互作用。此外，LUG在酵母和植物细胞中的几个异源启动子上表现出很强的抑制活性。相比之下，SEU不表现出任何直接的抑制活性，但仅在存在LUG的情况下才能抑制报告基因的表达，这表明SEU可能作为LUG的衔接蛋白发挥作用。我们的结果表明，LUG编码Tup1的功能同源物，并且SEU的功能可能类似于Tup1的衔接蛋白Ssn6。我们已经确定LUG的LUG/LUH、Flo8、单链DNA结合蛋白结构域对于与SEU的相互作用是必要且充分的，并且LUG的两个结构域对于其抑制功能很重要。我们的工作为植物转录共抑制因子提供了功能见解，并揭示了植物共抑制因子与酵母和动物共抑制因子之间的保守性和区别。
