The human SETMAR protein preserves most of the activities of the ancestral Hsmar1 transposase
The human SETMAR protein preserves most of the activities of the ancestral Hsmar1 transposase
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DOI：
10.1128/mcb.01899-06
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发表时间：
2007-02-01
影响因子：
5.3
通讯作者：
Chalmers, Ronald
中科院分区：
文献类型：
--
作者：
Liu, Danxu;Bischerour, Julien;Chalmers, Ronald
转座子为大量人类基因提供了蛋白质编码序列。除 V(D)J 重组酶和端粒酶外，所有酶的功能仍未知。在这里，我们研究了人类 SETMAR 蛋白的活性，这是一种组蛋白 H3 甲基化酶和水手家族转座酶之间高表达的融合蛋白。尽管 SETMAR 已表现出甲基化酶活性和 DNA 修复表型，但其作用模式和转座酶结构域的作用仍然不清楚。作为解决这个问题的起点，我们在全长蛋白质和分离的转座酶结构域的背景下剖析了转座酶结构域的活性。检测到转座酶结构域对工程化 Hsmar1 转座子的完全转座，尽管反应的程度受到元件 3' 端切割的严重缺陷的限制。尽管存在这个问题，SETMAR 在 Hsmar1 转座反应的其他阶段仍保留了强大的活性，即位点特异性 DNA 与转座子末端的结合、配对末端复合物的组装、Mn2+ 元件 5' 末端的切割以及 TA 二核苷酸靶位点的整合。尽管切口活性可能在 DNA 修复表型中发挥作用，但 SETMAR 不太可能催化人类基因组中的转座。因此，mariner 结构域的关键活性是强大的 DNA 结合和环化活性，该活性非常有可能将组蛋白甲基化酶结构域靶向人类基因组中由 Hsmar1 转座子副本提供的数千个特异性结合位点。
Transposons have contributed protein coding sequences to a unexpectedly large number of human genes. Except for the V(D)J recombinase and telomerase, all remain of unknown function. Here we investigate the activity of the human SETMAR protein, a highly expressed fusion between a histone H3 methylase and a mariner family transposase. Although SETMAR has demonstrated methylase activity and a DNA repair phenotype, its mode of action and the role of the transposase domain remain obscure. As a starting point to address this problem, we have dissected the activity of the transposase domain in the context of the full-length protein and the isolated transposase domain. Complete transposition of an engineered Hsmar1 transposon by the transposase domain was detected, although the extent of the reaction was limited by a severe defect for cleavage at the 3' ends of the element. Despite this problem, SETMAR retains robust activity for the other stages of the Hsmar1 transposition reaction, namely, site-specific DNA binding to the transposon ends, assembly of a paired-ends complex, cleavage of the 5' end of the element in Mn2+, and integration at a TA dinucleotide target site. SETMAR is unlikely to catalyze transposition in the human genome, although the nicking activity may have a role in the DNA repair phenotype. The key activity for the mariner domain is therefore the robust DNA-binding and looping activity which has a high potential for targeting the histone methylase domain to the many thousands of specific binding sites in the human genome provided by copies of the Hsmar1 transposon.