Progression through the cell cycle is driven by cyclin-dependent kinases (CDKs) whose activity is controlled by regulatory subunits called cyclins. The expression of cyclins is subject to numerous controls at multiple levels, not least at the level of transcription. As a first step to unravel the mechanisms that regulate expression of B-cyclins in plants, we undertook the identification of the required promoter elements of the Arath;CycB1;1 gene. A detailed analysis of different promoter fragments consisted in analysing their ability to mediate cell cycle-dependent transcriptional oscillations of the gus reporter gene in transformed BY-2 cell lines. We showed that different promoter regions took part in transcriptional activation. Furthermore, 202 bp upstream of the ATG were sufficient to induce M-phase-specific expression. This region contains an 18 bp sequence including a Myb-binding core (AACGG) which is able to activate reporter gene without leading to M-phase-specific expression. Electrophoretic mobility shift assays showed that this 18 bp sequence specifically binds protein complexes from Arabidopsis cell suspension enriched either in G1 or G2 phase. Furthermore, the Myb core, AACGG, was characterized as necessary for the binding of proteins. DNA affinity purification of the complexes bound to the 18 bp sequence allowed the isolation of three different complexes and two proteins from these complexes were identified by mass spectrometry analyses. A new putative Myb transcription factor and a hypothetical protein, HYP containing with a leucine zipper and Myc-type dimerization domains were identified. When over-expressed in plants, HYP factor is able to trans-activate the expression of gus reporter gene downstream from the -202 promoter fragment as well as the endogenous CycB1;1 gene.

中文翻译：

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Arath; CycB1; 1转录和推定调节蛋白的鉴定中涉及与细胞周期阶段无关的激活的顺式作用元件的表征。

整个细胞周期的进展是由细胞周期蛋白依赖性激酶（CDK）驱动的，其活性受称为细胞周期蛋白的调节亚基控制。细胞周期蛋白的表达在多个水平上受到众多控制，尤其是在转录水平上。为揭示调节植物中B细胞周期蛋白表达的机制的第一步，我们进行了Arath; CycB1; 1基因所需启动子元件的鉴定。对不同启动子片段的详细分析包括分析它们在转化的BY-2细胞系中介导gus报道基因的细胞周期依赖性转录振荡的能力。我们表明不同的启动子区域参与转录激活。此外，ATG上游202 bp足以诱导M期特异性表达。该区域包含一个18 bp的序列，其中包含一个Myb结合核心（AACGG），该核心能够激活报告基因而不会导致M期特异性表达。电泳迁移率变动分析表明，该18 bp序列特异性结合了富含G1或G2相的拟南芥细胞悬液中的蛋白质复合物。此外，Myb核心AACGG被认为是蛋白质结合所必需的。结合至18 bp序列的复合物的DNA亲和纯化可分离出三种不同的复合物，并通过质谱分析从这些复合物中鉴定出两种蛋白质。确定了一个新的假定的Myb转录因子和一种假设蛋白HYP，该蛋白含有亮氨酸拉链和Myc型二聚结构域。当在植物中过度表达时，