Waksman Institute, Rutgers, The State University of New Jersey, PO Box 759, Piscataway, NJ 08855, USA.
Plant J. 1995 May;7(5):797-807.
map has been developed of nuclease-hypersensitive sites of P-rr, the standard allele of the P-locus of Zea mays L. Using a traditional DNase I assay, eight such sites have been found that are specific for the expressing tissue and span a region of more than 25 kb of the P-locus, making it one of the largest plant genes yet described. The maps of the standard allele have also been compared with the recently described moderately stable P-pr allele, which arose from epimutation. Six of the eight sites exhibit the same tissue-specificity in P-pr plants, while two stay repressed as in non-expressing tissues of plants with the standard allele. Interestingly, the two repressed sites coincide with two hypermethylated restriction sites that have previously been correlated with the expression potential of the P-pr allele. On the other hand, four of the DNase I sites, coinciding with CpG islands that were not hypermethylated by the epimutation, also showed no differences in their sensitivity to DNase I between the standard allele and the P-pr allele. This suggests that the epimutation affects both site-specific methylation changes and a specific local chromatin structure of the P gene involved in its regulation.
已经绘制出玉米 P 位点标准等位基因 P-rr 的核酸酶超敏位点图谱。使用传统的 DNA 酶 I 测定法，发现了 8 个这样的位点，它们是表达组织特异性的，跨越了 P 基因座的 25kb 以上的区域，使其成为迄今为止描述的最大的植物基因之一。标准等位基因的图谱也与最近描述的中度稳定的 P-pr 等位基因进行了比较，后者是由表型反转突变引起的。在 P-pr 植物中，这 8 个位点中的 6 个表现出相同的组织特异性，而另外 2 个在具有标准等位基因的植物的非表达组织中仍然受到抑制。有趣的是，这两个受抑制的位点与之前与 P-pr 等位基因表达潜力相关的两个超甲基化的限制位点相吻合。另一方面，与表型反转突变未发生超甲基化的 CpG 岛重合的 4 个 DNA 酶 I 位点，在标准等位基因和 P-pr 等位基因之间，对 DNA 酶 I 的敏感性也没有差异。这表明，表型反转突变既影响特定的甲基化变化，也影响参与其调控的 P 基因的特定局部染色质结构。
