Sardana R, O'Dell M, Flavell R
Department of Molecular Genetics, Cambridge Laboratory, Norwich, UK.
Mol Gen Genet. 1993 Jan;236(2-3):155-62. doi: 10.1007/BF00277107.
A large number of wheat rRNA genes are methylated at all the CCGG sites that are present in the intergenic regions. A smaller number of rRNA genes are not methylated at one or more CCGG sites. A subset of genes was found unmethylated at a specific CCGG site just downstream of the array of 135 bp A repeats in the intergenic region. In all the genotypes studied, the rDNA loci with larger intergenic regions between their genes also possess a greater number of rRNA genes that are unmethylated at one or more CCGG sites in the intergenic regions than do the loci with shorter intergenic regions. In four genotypes (for which data were available), rDNA loci with longer intergenic regions had larger secondary constrictions on metaphase chromosomes, a measure of relative locus activity, than the loci with shorter intergenic regions. The results have been integrated into a model for the control of rDNA expression based on correlations between cytosine methylation patterns and the number of upstream 135 bp repeats in intergenic regions. According to this model the 135 bp repeats play a part in the control of gene activity by binding a protein(s) that is in limiting supply, thereby predisposing the neighbouring gene to become active preferentially.
大量小麦核糖体RNA基因在基因间区域存在的所有CCGG位点处发生甲基化。少数核糖体RNA基因在一个或多个CCGG位点未发生甲基化。在基因间区域135 bp A重复序列阵列下游的一个特定CCGG位点发现了一部分未甲基化的基因。在所有研究的基因型中，与基因间区域较短的位点相比，基因间区域较大的核糖体DNA位点在基因间区域一个或多个CCGG位点未甲基化的核糖体RNA基因数量也更多。在四种有数据的基因型中，与基因间区域较短的位点相比，基因间区域较长的核糖体DNA位点在中期染色体上具有更大的次缢痕，这是相对位点活性的一种衡量。基于胞嘧啶甲基化模式与基因间区域上游135 bp重复序列数量之间的相关性，这些结果已被整合到一个核糖体DNA表达调控模型中。根据这个模型，135 bp重复序列通过结合一种供应有限的蛋白质来参与基因活性的调控，从而使相邻基因优先变得活跃。
