Molecular Mechanism of Regulation of Cell Cycle-Dependent Gene Expression in Higher Plants

为了阐明高等植物细胞分裂周期中S期特异转录调控的分子机制，我和我的同事研究了与小麦组蛋白H3基因转录调控有关的顺式作用元件和反式作用因子的结构和功能。在本研究中，我们取得了以下成果。作为H3基因转录S相特异性的顺式元件，我们在H3启动子-185区域的三个顺式元件中鉴定出两个基序(六聚体和八聚体序列)。我们已经鉴定出与六聚体基序相互作用的序列特异性DNA结合蛋白HBP-1a和HBP-1b。分离编码每种蛋白的CDNA克隆并测定其核苷酸序列。由核苷酸序列推导的氨基酸序列表明，HBP-1a和-1b在氨基和羧基末端附近分别具有bZIP基序。我们还鉴定了一个DNA结合蛋白HBP-2，它与另一个顺式元件--九聚体序列特异地相互作用，并且该蛋白具有锌指基序。为了研究HBP-1a和HBP-1b的功能，我们在水稻和烟草细胞培养的瞬时表达系统中检测了由CaMV 35S启动子和HBP-1a或-1b Edna组成的效应基因对含有H3启动子/GUS编码区的报告基因表达的影响。我们已经获得的证据表明，这两种蛋白都是参与H3基因转录的调节因子。我们在克隆的HBP-1a和-1b基因的启动子区域发现了六聚体和类六聚体基序，并观察到这些基序可以与HBP-1a和-1b结合。提示这些基因的转录可能受因子自身的自身调节。

In order to elucidate the molecular mechanisms of S-phase-specific transcription regulation in the division cycle of higher plant cells, my co-workers and I have studied the structures and functions of cis-acting elements and trans-acting factors which are implicated in the regulation of the wheat histone H3 gene transcription. We have obtained the following results in this research.1. As cis-elements for the S-phase specificity of the H3 gene transcription we have identified two motifs (hexamer and octamer sequences) in three cis-elements located within the -185 region of the H3 promoter.2. We have identified the sequence-specific DNA-binding proteins, HBP-1a and HBP-1b, that are interact with the hexamer motif. The CDNA clones encoding each of proteins were isolated and their nucleotide sequences were determined. The amino acid sequences deduced from the nucleotide sequences suggested that the HBP-la and -1b have a bZIP motif at the regions near the amino- and carboxy-termini, respectively. We also have identified a DNA-binding protein, HBP-2, which specifically interacts with another cis-element, nonamer sequence, and this protein was shown to have a Zn-finger motif.3. To study the function of HBP-1a and -1b, we examined the influence of the effector gene consisting of the CaMV 35S promoter and HBP-1a or -1b EDNA on the expression of the reporter gene containing the H3 promoter/GUS coding region in the transient expression system using rice and tabacco cell cultures. We have obtained evidence that the proteins both are regulatory factors involved in the H3 gene transcription.4. We found the hexamer and hexamer-like motifs in the promoter regions of cloned HBP-1a and -1b genes and observed that the motifs can bind HBP-1a and -1b. It is suggested that transcription of these genes may be autoregulated by the factors themselves.