Foley R C, Grossman C, Ellis J G, Llewellyn D J, Dennis E S, Peacock W J, Singh K B
Department of Biology, University of California, Los Angeles 90024.
Plant J. 1993 May;3(5):669-79.
Ocs-elements, a family of 20 bp DNA sequences, are components of a number of promoters active in plants. In the maize BMS cell line the dominant ocs-element binding activity is the ocs-element transcription factor complex called OTF. The isolation of cDNA clones from a BMS cDNA expression library for two bZIP (basic region-leucine zipper) proteins that bind the ocs-element sequence and are good candidates for forming at least part of OTF is described. The two ocs-element binding proteins, called OBF3.1 and OBF3.2, are closely related, with the OBF3.1 protein sharing 95.8% amino acid homology with part of the OBF3.2 protein although there were significant differences in the 3' untranslated regions. Genomic Southern blot analysis revealed a small gene family with a minimum of two OBF3 loci mapping to chromosomes 3L105 and 8L075. The OBF3.1 protein shared considerable homology with the wheat HBP1b protein (80% amino acid identity) and to a lesser extent with the tobacco TGA1aa protein. OBF3.1 like HBP1b was able to bind well to the Hex sequence but poorly to G-box/ABRE sequences. Interestingly, OBF3.1 bound eightfold more efficiently to an ocs-element sequence than TGA1a, raising the possibility that OBF3.1 and TGA1a may be distinct members of an OBF3/TGA subfamily.
ocs元件是一类20bp的DNA序列，是植物中许多活跃启动子的组成部分。在玉米BMS细胞系中，占主导地位的ocs元件结合活性是一种名为OTF的ocs元件转录因子复合体。本文描述了从BMS cDNA表达文库中分离出两个与ocs元件序列结合的bZIP（碱性区域-亮氨酸拉链）蛋白的cDNA克隆，它们很可能是构成OTF至少一部分的候选蛋白。这两个与ocs元件结合的蛋白分别称为OBF3.1和OBF3.2，它们密切相关，OBF3.1蛋白与OBF3.2蛋白的一部分具有95.8%的氨基酸同源性，尽管它们的3'非翻译区存在显著差异。基因组Southern杂交分析显示存在一个小基因家族，至少有两个OBF3基因座定位于3L105和8L075染色体上。OBF3.1蛋白与小麦HBP1b蛋白具有相当高的同源性（80%氨基酸同一性），与烟草TGA1aa蛋白的同源性较低。与HBP1b一样，OBF3.1能够很好地结合Hex序列，但与G-box/ABRE序列的结合能力较差。有趣的是，OBF3.1与ocs元件序列的结合效率比TGA1a高八倍，这增加了OBF3.1和TGA1a可能是OBF3/TGA亚家族不同成员的可能性。
