Paramutation of the Maize R Gene

玉米R基因的有色种子等位基因大多是亚稳态的。色素沉着通过与某些等位基因的杂合性（参数化）遗传地减少，而在其他组合中遗传地增加。这些变化是几代人累积起来的。使用对胞嘧啶甲基化敏感的限制性内切酶的探索性试验表明，辅助R等位基因的DNA R区存在高甲基化。我们建议在经历参数化的最不复杂的等位基因中描述这种变化，利用一系列渐变的色素沉着水平，包括增强状态和减少状态。从DNA修饰方面表征R作用的其他现象包括：烷基化剂对R着色的显著影响，通过花粉和胚珠传播后R着色水平的差异，以及R植物着色的参数化依赖于等位基因复合体中种子颜色成分的存在。负责诱导参数化的成分已经在R点等位基因中被定位为遗传特征，将被分子表征。参数化是一种遗传现象，至今还没有分子的解释。在这个系统中，作为任何生物体中最容易理解的参数化的例子，有迹象表明DNA的甲基化参与其中。本研究的结果将进一步深入了解基因表达的机制，并可能促进基因工程的商业应用。

Most colored-seed alleles of the maize R gene are metastable. Pigmentation is reduced heritably by heterozygosity with certain alleles (paramutation) and increased heritably in still other combinations. The changes are cumulative over generations. Exploratory tests using restriction enzymes whose action is sensitive to cytosine methylation indicate hypermethylation in the R region of DNA from paramutant R alleles. We propose to characterize this change in the least complex alleles that undergo paramutation, utilizing a graded series of pigmentation levels that includes enhanced as well as reduced states. Other phenomena of R action to be characterized in terms of DNA modification include: a marked influence of alkylating agents on R paramutation, differences in R pigmentation level following transmission through pollen and ovule, and the dependence of paramutation of R plant pigmentation on presence of seed-color component in the allelic complex. Components responsible for inducing paramutation that have been mapped genetically in the R- stippled allele are to be characterized molecularly. Paramutation is a genetic phenomena for which there is as yet no molecular explanation. In this system the best understood example of paramutation in any organism, indications are that methylation of the DNA is involved. Results from this study should provide further insight into the mechanisms involved in gene expression and may enhance commercial applications of genetic engineering.