Talbert L E, Chandler V L
Institute of Molecular Biology, University of Oregon, Eugene 97403.
Mol Biol Evol. 1988 Sep;5(5):519-29. doi: 10.1093/oxfordjournals.molbev.a040510.
Mutator stocks of maize exhibit a high mutation rate correlated with the activity of a family of transposable elements. Mu1 and, to a lesser extent, the closely related Mu1.7 elements are responsible for most mutator-induced mutations that have been characterized. These elements are found in 10-60 copies in mutator stocks, and zero to a few intact elements exist in nonmutator maize stocks. Additionally, the component parts of Mu elements exist separately in the maize genome. The Mu terminal inverted repeats are found in multiple copies in all maize lines and related Zea species tested, and Mu internal sequences exist unassociated with Mu termini. In the present paper, we describe the structure and genomic distribution of one Mu-homologous sequence termed MRS-A (for Mu-related sequence). DNA sequencing shows that MRS-A is closely related to the internal region of Mu1 and Mu1.7 elements. However, it has no Mu termini and does not have the structure of a transposable element. This sequence is present in one or two copies in all maize lines and is highly conserved in the genus Zea. A similar sequence exists in a species within the genus most closely related to Zea, Tripsacum dactyloides, although the T. dactyloides genome does not contain any Mu termini or intact Mu elements. Furthermore, an RNA transcript homologous to MRS-A and its flanking DNA is found in both mutator and nonmutator maize plants. These results suggest that MRS-A represents a stable, functional region of the maize genome, and we speculate that a similar sequence was encompassed by Mu termini to generate a Mu transposable element.
玉米的突变体株系表现出与一类转座元件的活性相关的高突变率。Mu1以及在较小程度上与之密切相关的Mu1.7元件是大多数已被表征的突变体诱导突变的原因。这些元件在突变体株系中以10 - 60个拷贝存在，而在非突变体玉米株系中存在零至少数完整元件。此外，Mu元件的组成部分在玉米基因组中是分开存在的。Mu末端反向重复序列在所有测试的玉米品系和相关的玉米属物种中以多个拷贝存在，并且Mu内部序列独立于Mu末端存在。在本文中，我们描述了一个称为MRS - A（Mu相关序列）的Mu同源序列的结构和基因组分布。DNA测序表明MRS - A与Mu1和Mu1.7元件的内部区域密切相关。然而，它没有Mu末端，也不具有转座元件的结构。该序列在所有玉米品系中以一或两个拷贝存在，并且在玉米属中高度保守。在与玉米最密切相关的属中的一个物种大刍草（Tripsacum dactyloides）中存在类似序列，尽管大刍草基因组不包含任何Mu末端或完整的Mu元件。此外，在突变体和非突变体玉米植株中都发现了与MRS - A及其侧翼DNA同源的RNA转录本。这些结果表明MRS - A代表了玉米基因组的一个稳定的功能区域，并且我们推测一个类似的序列被Mu末端包围以产生一个Mu转座元件。
