Lam E, Chua N H
Laboratory of Plant Molecular Biology, Rockefeller University, New York, NY 10021.
Science. 1990 Apr 27;248(4954):471-4. doi: 10.1126/science.2330508.
Light-dependent expression of rbcS, the gene encoding the small subunit of ribulose-1,5-bisphosphate carboxylase, which is the key enzyme involved in carbon fixation in higher plants, is regulated at the transcriptional level. Sequence analysis of the gene has uncovered a conserved GT motif in the -150 to -100 region of many rbcS promoters. This motif serves as the binding site of a nuclear factor, designated GT-1. Analysis of site-specific mutants of pea rbcS-3A promoter demonstrated that GT-1 binding in vitro is correlated with light-responsive expression of the rbcS promoter in transgenic plants. However, it is not known whether factors other than GT-1 might also be required for activation of transcription by light. A synthetic tetramer of box II (TGTGTGGTTAATATG), the GT-1 binding site located between -152 to -138 of the rbcS-3A promoter, inserted upstream of a truncated cauliflower mosaic virus 35S promoter is sufficient to confer expression in leaves of transgenic tobacco. This expression occurs principally in chloroplast-containing cells, is induced by light, and is correlated with the ability of box II to bind GT-1 in vitro. The data show that the binding site for GT-1 is likely to be a part of the molecular light switch for rbcS activation.
核酮糖-1,5-二磷酸羧化酶小亚基基因（rbcS）的表达依赖于光，该酶是高等植物碳固定过程中的关键酶，其表达在转录水平受到调控。对该基因的序列分析发现，许多rbcS启动子的-150至-100区域存在一个保守的GT基序。这个基序是一种名为GT-1的核因子的结合位点。对豌豆rbcS-3A启动子的位点特异性突变体分析表明，GT-1在体外的结合与转基因植物中rbcS启动子的光响应表达相关。然而，尚不清楚除GT-1之外的其他因子是否也是光激活转录所必需的。位于rbcS-3A启动子-152至-138之间的GT-1结合位点盒II（TGTGTGGTTAATATG）的合成四聚体，插入到截短的花椰菜花叶病毒35S启动子上游，足以在转基因烟草叶片中赋予表达。这种表达主要发生在含叶绿体的细胞中，受光诱导，并且与盒II在体外结合GT-1的能力相关。数据表明，GT-1的结合位点可能是rbcS激活的分子光开关的一部分。
