Butler Matthew G, Chakraborty Sangita A, Lampe David J
Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109, USA.
Genetica. 2006 May;127(1-3):351-66. doi: 10.1007/s10709-006-6250-x.
Mariner family transposons are perhaps the most widespread transposable elements of eukaryotes. While we are beginning to understand the precise mechanism of transposition of these elements, the structure of their transposases are still poorly understood. We undertook an extensive mutagenesis of the N-terminal third of the transposase of the Himar1 mariner transposon to begin the process of determining the structure and evolution of mariner transposases. N and C-terminal deletion analyses localized the DNA binding domain of Himar1 transposase to the first 115 amino acids. Alanine scanning of 23 selected sites within this region uncovered mutations that not only affected DNA binding but DNA cleavage as well. The behavior of other mutations strongly suggested that the N-terminus is also involved in multimerization of the transposase on a single inverted terminal repeat and in paired ends complex formation which brings together the two ends of the transposon. Finally, two hyperactive mutations at conserved sites suggest that mariner transposases are under a pattern of stabilizing selection in nature with regard to how efficiently they mediate transposition, resulting in a population of "average" transposons.
水手家族转座子可能是真核生物中分布最广泛的转座元件。虽然我们开始了解这些元件转座的精确机制，但其转座酶的结构仍知之甚少。我们对希马尔1号水手转座子转座酶的N端三分之一进行了广泛的诱变，以开始确定水手转座酶的结构和进化过程。N端和C端缺失分析将希马尔1号转座酶的DNA结合结构域定位到前115个氨基酸。对该区域内23个选定位点的丙氨酸扫描发现了不仅影响DNA结合而且影响DNA切割的突变。其他突变的行为强烈表明，N端也参与转座酶在单个反向末端重复序列上的多聚化以及将转座子两端聚集在一起的配对末端复合物的形成。最后，保守位点的两个高活性突变表明，就介导转座的效率而言，水手转座酶在自然界中处于稳定选择模式，从而产生了一群“平均”转座子。
