ISOLATION OF THE B GENE: A REGULATORY LOCUS IN MAIZE

了解基因是如何在生物进化过程中受到差异调控的 生物体的发育是生物学中的一个基本问题。 对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，并已发现 转座元件效应等调控现象 关于基因表达和节约化。从基因上来说就是这样 玉米中特有的基因座是B，它调控着基因的表达 植物中的紫色花青素色素。中的变化 花色苷的发育时序和组织特异性 合成是由B出现的等位基因决定的。 在分子水平上不同的B等位基因应该揭示核苷酸 负责调节时间和组织的序列- 颜料生产的专一性。某些B等位基因会经历或 促进变态：基因表达的一种可遗传改变 由于同一植物中存在两个特定的等位基因而促进的。 已经提出了许多模型来解释参数化，包括 基因转换，染色质结构的改变，DNA 修饰，或DNA元素的相互作用或转位。 对这种等位基因相互作用的分子描述应该揭示 细胞可遗传调控基因表达的一般原理 因为它发生在发育过程中。这些原则应该是 适用于基因和基因相结合的其他生物体 分子方法还不可行。 长期目标是研究分子机制。 控制B的表达本提案的具体目的 是利用转座元件克隆B基因组序列 并使用克隆的序列和突变体开始分析 B.多重独立插入的结构和功能 突变体和返回体已经被分离出来。变种人和 从它们分离出来的返回体，具有不同的表型 到合成色素的组织。插入 一种元素进入B将产生一种分离的分子标记 具有突变表型。该元素和邻近的基因将 的同源性进行恢复 插入B基因的元件和克隆的转座子 元素。然后，克隆的序列将被用于确定 野生型和突变型B等位基因AS的结构和表达 以及辅助减支的分子基础。

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.