Schindler U, Menkens A E, Beckmann H, Ecker J R, Cashmore A R
University of Pennsylvania, Department of Biology, Philadelphia 19104-6018.
EMBO J. 1992 Apr;11(4):1261-73. doi: 10.1002/j.1460-2075.1992.tb05170.x.
The promoters of a variety of plant genes are characterized by the presence of a G-box (CCACGTGG) or closely related DNA motifs. These genes often exhibit quite diverse expression characteristics and in many cases the G-box sequence has been demonstrated to be essential for expression. The G-box of the Arabidopsis rbcS-1A gene is bound by a protein, GBF, identified in plant nuclear extracts. Here we report the isolation of three Arabidopsis thaliana cDNA clones encoding GBF proteins referred to as GBF1, GBF2 and GBF3. GBF1 and GBF2 mRNA is present in light and dark grown leaves as well as in roots. In contrast, GBF3 mRNA is found mainly in dark grown leaves and in roots. The deduced amino acid sequences of the three cDNAs indicate that each encodes a basic/leucine zipper protein. In addition, all three proteins are characterized by an N-terminal proline-rich domain. Homodimers of the three proteins specifically recognize the G-box motif, with GBF1 and GBF3 binding symmetrically to this palindromic sequence. In contrast, GBF2 binds to the symmetrical G-box sequence in such a way that the juxtaposition of the protein and the DNA element is clearly asymmetric and hence distinct from that observed for the other two proteins. The fact that GBF1, GBF2 and GBF3 possess both distinct DNA binding properties and expression characteristics prompt us to entertain the notion that these proteins may individually mediate distinct subclasses of expression properties assigned to the G-box. Furthermore, we demonstrate that GBF1, GBF2 and GBF3 heterodimerize and these heterodimers also interact with the G-box, suggesting a potential mechanism for generating additional diversity from these GBF proteins.
多种植物基因的启动子的特征是存在一个G盒（CCACGTGG）或与之密切相关的DNA基序。这些基因通常表现出相当多样的表达特征，并且在许多情况下，G盒序列已被证明对表达至关重要。拟南芥rbcS - 1A基因的G盒与一种在植物核提取物中鉴定出的蛋白质GBF结合。在此，我们报告了三个拟南芥cDNA克隆的分离，这些克隆编码的GBF蛋白分别称为GBF1、GBF2和GBF3。GBF1和GBF2的mRNA在光照和黑暗条件下生长的叶片以及根中均有存在。相比之下，GBF3的mRNA主要在黑暗条件下生长的叶片和根中发现。这三个cDNA推导的氨基酸序列表明，每个序列都编码一种碱性/亮氨酸拉链蛋白。此外，所有这三种蛋白质的特征都是具有一个富含脯氨酸的N端结构域。这三种蛋白质的同源二聚体特异性识别G盒基序，GBF1和GBF3对称地结合到这个回文序列上。相比之下，GBF2以这样一种方式结合到对称的G盒序列上，即蛋白质与DNA元件的并列明显不对称，因此与其他两种蛋白质观察到的情况不同。GBF1、GBF2和GBF3具有不同的DNA结合特性和表达特征这一事实促使我们考虑这样一种观点，即这些蛋白质可能分别介导赋予G盒的不同表达特性亚类。此外，我们证明GBF1、GBF2和GBF3能形成异源二聚体，并且这些异源二聚体也与G盒相互作用，这表明了一种从这些GBF蛋白产生额外多样性的潜在机制。
