The Mu Transposons

对于任何转座元件系统来说，必须回答的最基本的问题可能是：“是什么编码了自主(转座酶)功能，它是如何传递的？”这是我们在玉米Mu转座子系统中解决的主要问题。提出了五种不同的方法。1)一个新发现的Mu转座子在结构上与自主一致。这种元素将使用T-DNA添加到烟草试管苗的一种特殊测试品系中：如果转座子是自主的，它将指定“激活酶”，使烟草基因恢复，从而获得抗卡那霉素的烟草。类似的实验也将在玉米细胞上进行。2)我们最近发现一些Mu转座子具有圆形。这些将被显微注射到试验者烟草品系和玉米中。3)新的Mu转座子的特征。4)我们将使用一系列的遗传杂交来评估Mu拷贝数控制的假说，并通过选择罕见的“相变”表型来获得影响Mu切除的突变体。5)我们还建议通过寻找特定的蛋白-Mu结合来直接鉴定转座酶。第二个目标涉及Mu切除产品的特征。在这些拟议的实验中寻求的信息不仅对我们理解这个真正独特的转座子系统至关重要，而且如果Mu要用于生物技术，也是必不可少的。

Perhaps the most fundamental question that must be answered for any transposable element system is: "What encodes the autonomous (transposase) function and how is it transmitted?" That is the primary question we address for the Mu transposon system in maize. Five different approaches are proposed. 1) A newly discovered Mu transposon is structurally consistent with autonomy. The element will be added using T-DNA to a special tester line of tobacco plantlets: If the transposon is autonomous it will specify "excisase" that will revert a tobacco gene, leading to a kanomycin-resistent tobacco. A similar experiment will be done using maize cells. 2) We recently discovered that some Mu transposons have circular forms. These will be microinjected into the tester tobacco line and into maize. 3) New Mu transposons will be characterized. 4) We will use a series of genetic crosses to evaluate hypotheses for Mu copy number control, and will also obtain mutants affecting Mu excision by selecting rare "phase change" phenotypes. 5) We also propose to identify the transposase directly by looking for specific protein-Mu binding. A secondary aim involves characterization of Mu excision products. The information sought in these proposed experiments is not only essential for our understanding of this truly unique transposon system, but is essential if Mu is to be useful for biotechnology.