ISOLATION OF THE B GENE: A REGULATORY LOCUS IN MAIZE

了解基因在细胞周期中的差异调节 生物体的发育是生物学中的一个基本问题。 玉米的遗传研究提供了许多程序化的例子， 在发育过程中基因表达的变化， 调节现象，如转座因子的作用 基因表达和副突变。 一个这样的基因 在玉米中的特征位点是B，其调节 植物中的紫色花青素色素。 变化 花色素苷的发育时间和组织特异性 合成取决于在B上存在哪个等位基因。 检查 不同的B等位基因在分子水平上应该揭示核苷酸 负责调节时间和组织的序列- 色素生产的特异性。 某些B等位基因经历或 促进副突变：基因表达的一种可遗传的改变 由同一植物中两个特定等位基因的存在促进。 许多模型已经被提出来解释副突变，包括 基因转换，染色质结构改变，DNA 修饰，或DNA元件的相互作用或转座。 这种等位基因相互作用的分子描述应该揭示 基因表达的细胞遗传调节的一般原理 因为它发生在发育过程中。 这些原则应该是 适用于其他生物体， 分子方法尚不可行。 长期目标是研究分子机制 控制B的表达。 本提案的具体目标 是用转座因子克隆B基因组序列 并使用克隆的序列和突变体来开始分析 B结构和功能。 多重独立插入 突变体和回复突变体已经被分离出来。 变种人和 从它们分离的回复突变体，具有不同的表型， 到合成色素的组织。 的插入 一个元素进入B会产生一个分子标记， 突变体表型。 该元件和邻近的基因将 通过利用 插入到B基因中的元件和克隆的转座因子 元素 然后将使用克隆的序列来确定 野生型和突变型B等位基因的结构和表达， 以及副突变的分子基础。

Understanding how genes are differentially regulated during the development of an organism is a fundamental problem in biology. Genetic studies of maize have provided many examples of programmed changes in gene expression during development and have identified regulatory phenomena such as the effects of transposable elements on gene expression and paramutation. One such genetically characterized locus in maize is B, which regulates the expression of the purple anthocyanin pigments in the plant. Variation in the developmental timing and tissue-specificity of anthocyanin synthesis is determined by which allele is present at B. Examining different B alleles at the molecular level should reveal nucleotide sequences responsible for regulating the timing and tissue- specificity of pigment production. Certain B alleles undergo or promote paramutation: a heritable alteration in gene expression promoted by the presence of two specific alleles in the same plant. Many models have been proposed to explain paramutation, including gene conversion, alterations in chromatin structure, DNA modification, or the interaction or transposition of DNA elements. A molecular description of this allelic interaction should reveal general principles on cell heritable regulation of gene expression as it occurs during development. These principles should be applicable to other organisms where a combined genetic and molecular approach is not yet feasible. The long term goals are to examine the molecular mechanisms controlling the expression of B. The specific aim of this proposal is to clone the B genomic sequences using transposable elements and to use the cloned sequences and mutants to begin analyzing the structure and function of B. Multiple independent insertion mutants and revertants have been isolated. The mutants and revertants isolated from them, have varied phenotypes with respect to the tissues in which pigment is synthesized. The insertion of an element into B will produce a molecular marker that segregates with the mutant phenotype. The element and the adjacent gene will be recovered by taking advantage of the homology between the element inserted into the B gene and the cloned transposable element. The cloned sequences will then be used to determine the structure and expression of the wild type and mutant B alleles as well as the molecular basis for paramutation.