Paramutation of the Maize R Gene

玉米R基因的大多数有色种子等位基因是亚稳定的。色素沉着由于某些等位基因的杂合性(参数突变)而遗传性减少，而在其他组合中遗传性增加。这些变化是世代累积的。使用对胞嘧啶甲基化敏感的限制性内切酶的探索性测试表明，DNA的R区高甲基化来自辅助突变的R等位基因。我们建议利用包括增强状态和降低状态在内的一系列分级的色素沉着水平，在经历参数改变的最不复杂的等位基因中描述这种变化。其他需要用DNA修饰来表征的R作用现象包括：烷化剂对R参变的显著影响，R通过花粉和胚珠传递后R色素水平的差异，以及R植物色泽的参变依赖于等位基因复合体中种子颜色成分的存在。在R-点状等位基因中被基因定位的负责诱导参数突变的成分将被分子学表征。突变是一种遗传现象，目前尚无分子解释。在这个系统中，作为任何生物体中最好理解的辅助节律的例子，有迹象表明DNA的甲基化参与了。这项研究的结果应该会进一步深入了解基因表达所涉及的机制，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.