Allele Interactions that Heritably Alter Transcription

9603638玉米的b调控基因编码一个碱性-螺旋-环-螺旋蛋白，它与其他调控蛋白一起激活编码花青素生物合成酶的基因的转录。不同的b等位基因在不同的组织和不同的发育时期激活了这条途径。由于等位基因的表达是不同的，产生的色素的数量是调节蛋白水平的敏感指标，因此可以在植物水平上研究这种表达。已经发现，当特定的等位基因与其他等位基因在同一基因组中时，可以稳定地改变第二等位基因，这种改变不能用孟德尔的概念来解释。给这种现象起的名字是参数化法。以前的研究表明，b的参变所需的序列与该基因紧密连锁，位于5‘侧翼区域。然而，DNA测序和广泛的限制图谱并没有确定b等位基因在参数突变过程中的结构差异。提出了两个模型，并设计实验对模型进行了验证。一种模式是单向基因转化，这与改变的等位基因的稳定性是一致的。另一种模型表明，染色质结构的变化可能会导致可遗传的转录变化，这种变化发生在参数突变过程中。要问的问题是：哪些顺式作用序列和其他基因参与了参数突变？B转录需要哪些顺式作用位点？染色质、DNA甲基化或结构差异是否与截肢相关？异位位置的b序列能参与参数转换吗？为了确定顺式作用位点和反式作用位点，人们提出了各种突变策略，以确定建立或维持顺式突变和b转录所需的位置。非技术性转录可以通过染色体位置或接触交替的等位基因来改变，这表明基因不仅仅受到局部顺式作用序列和与这些序列相互作用的因素的调控。染色质环境调控基因表达的例子来自哺乳动物X染色体失活、基因组印迹、酵母交配型基因座沉默、果蝇位置效应变异、植物中的辅助突变和基因沉默等研究。机制在任何系统中都不清楚，尽管有证据表明可能涉及DNA或染色质修饰，或两者兼有。拟议中的研究旨在探索改变玉米调控基因转录的等位基因相互作用，应该有助于解决这一缺陷。

9603638 Chandler Technical The b regulatory gene of maize encodes a basic-helix-loop-helix protein, which together with other regulatory proteins, activates the transcription of genes encoding the anthocyanin biosynthetic enzymes. Different b alleles activate the pathway in distinct tissues and at different developmental times. Because the alleles are differentially expressed and the amount of pigment produced is a sensitive indicator of regulatory protein levels, such expression can be studied at the plant level. It has been found that specific alleles, when in the same genome with other alleles can alter the second allele in a stable fashion and such alteration cannot be explained by Mendelian concepts. The name given to such phenomena is paramutation. Previous studies have shown that the sequences required for paramutation of b are tightly linked to the locus and lie in the 5' flanking region. However, DNA sequencing and extensive restriction mapping have not identified structural differences between the b alleles undergoing paramutation. Two models are proposed and experiments are devised to test the models. One model is that of unidirectional gene conversion which is consistent with the stability of the altered allele. The other model suggests that changes in chromatin structure may cause the heritable alterations in transcription that occur during paramutation. Questions to be asked are: What cis-acting sequences and other genes participate in paramutation? What cis-acting sites are required for b transcription? Do chromatin, DNA methylation or structural differences correlate with paramutation? Are b sequences in ectopic locations able to participate in paramutation? A variety of mutagenesis strategies are proposed to identify cis-acting sites and trans-acting loci required for the establishment or maintenance of paramutation and for b transcription. Non-technical Transcription can be altered by chromosome position or exposure to alternate alleles, suggesting that genes are not regulated just by local cis-acting sequences and factors that interact with those sequences. Examples of chromatin environments regulating gene expression come from studies of mammalian X-chromosome inactivation, genome imprinting, silencing of yeast mating-type loci, position effect variegation in Drosophila, paramutation and gene silencing in plants. Mechanisms are not understood in any system, although evidence suggests that either DNA or chromatin modification, or both, could be involved. The proposed studies to probe allelic interactions that alter transcription at a corn regulatory gene should help to address this deficiency.