Walbot V, Britt A B, Luehrsen K, McLaughlin M, Warren C
Department of Biological Sciences, Stanford University, CA 94305.
Basic Life Sci. 1988;47:121-35. doi: 10.1007/978-1-4684-5550-2_9.
We discuss the properties of the Mutator (Mu) transposable element family of maize. We report the cloning of bz2-mu1, a mutable allele containing a 1.4-kb Mu element, using a combination of transposon tagging and tests for differential hybridization to northern and Southern blots. We report the sequence of this allele and the Mu element insertion, and propose a model for the structure of the Bz2 locus. We discuss the relationship between increased DNA modification of Mu elements and loss of somatic instability at bz2-mu1. To further explore this aspect of regulation of Mutator, we have used gene-specific probes to determine the level of modification at this locus in active and inactive Mutator lines. We have also utilized CsCl density gradients to estimate the overall level of DNA modification in active and inactive lines; we find that Mu elements in active lines are hypomethylated relative to other maize nuclear DNAs examined, and that in inactive lines the level of modification in Mu elements is similar to the genome as a whole. Utilizing gamma-irradiation, we have demonstrated that inactive lines can be reactivated; this reactivation is first noted as restitution of the spotted kernel phenotype characteristic of bz2-mu1 in active Mutator lines. Hybridization analysis of DNA from reactivated plants demonstrates that the Mu elements in general, and specifically the Mu element at bz2-mu1, have the lower level of DNA modification characteristic of active lines. These results are discussed in terms of the role and timing of DNA modification in regulating Mutator activities.
我们讨论了玉米Mutator（Mu）转座元件家族的特性。我们报告了bz2-mu1的克隆，它是一个含有1.4kb Mu元件的可变等位基因，采用了转座子标签技术与对Northern和Southern印迹进行差异杂交检测相结合的方法。我们报告了该等位基因和Mu元件插入的序列，并提出了Bz2基因座结构的模型。我们讨论了Mu元件DNA修饰增加与bz2-mu1体细胞不稳定性丧失之间的关系。为了进一步探索Mutator调控的这一方面，我们使用基因特异性探针来确定该基因座在活跃和不活跃Mutator系中的修饰水平。我们还利用CsCl密度梯度来估计活跃和不活跃系中DNA修饰的总体水平；我们发现，相对于所检测的其他玉米核DNA，活跃系中的Mu元件甲基化程度较低，而在不活跃系中，Mu元件的修饰水平与整个基因组相似。利用γ射线辐照，我们证明不活跃系可以被重新激活；这种重新激活首先表现为活跃Mutator系中bz2-mu1特有的斑点籽粒表型的恢复。对重新激活植株的DNA进行杂交分析表明，一般的Mu元件，特别是bz2-mu1处的Mu元件，具有活跃系特有的较低水平的DNA修饰。我们根据DNA修饰在调控Mutator活性中的作用和时间来讨论这些结果。
