Bryk M, Belisle M, Mueller J E, Belfort M
Molecular Genetics Program Wadsworth Center, State University of New York, New York State Department of Health, Albany 12201-0509, USA.
J Mol Biol. 1995 Mar 24;247(2):197-210. doi: 10.1006/jmbi.1994.0133.
I-TevI, a double-strand DNA endonuclease involved in the mobility of the td intron of phage T4, is highly unusual in that it binds and cleaves intronless td alleles (td homing sites) in a site-specific but sequence-tolerant manner. The endonuclease binds to sequences flanking the intron insertion site and near the remote cleavage site, located 23 and 25 nucleotides away on the top and bottom strands, respectively. Mapping studies indicate that I-TevI has both sequence and distance sensors that function during cut-site selection. Although I-TevI cleavage of many insertion and deletion variants of the homing site is impaired, double-strand breaks are generated at positions that collectively span two turns of the helix, indicating that the interaction is extraordinarily flexible. However, the endonuclease does exhibit spacing preferences between its binding domains, and sequence preferences near the cleavage site, with the G:C pair at -23 implicated as a cleavage determinant. Furthermore, I-TevI appears to function through interactions across the minor groove at the cleavage site, as it does at the intron insertion site, and to be capable of cleaving sequentially, first on the bottom and then on the top strand. These properties of I-TevI are incorporated in a model wherein the endonuclease effects distant cleavage via a flexible hinge.
I-TevI是一种参与噬菌体T4的td内含子移动的双链DNA内切酶，它非常独特，能够以位点特异性但序列容忍的方式结合并切割无内含子的td等位基因（td归巢位点）。该内切酶与内含子插入位点两侧以及远端切割位点附近的序列结合，远端切割位点分别位于上链和下链的23和25个核苷酸处。图谱研究表明，I-TevI具有在切割位点选择过程中起作用的序列和距离传感器。尽管I-TevI对归巢位点的许多插入和缺失变体的切割受到损害，但双链断裂在共同跨越螺旋两圈的位置产生，这表明这种相互作用非常灵活。然而，该内切酶在其结合结构域之间确实表现出间距偏好，并且在切割位点附近表现出序列偏好，其中-23处的G:C对被认为是切割决定因素。此外，I-TevI似乎通过在切割位点的小沟处进行相互作用来发挥作用，就像它在内含子插入位点那样，并且能够依次切割，首先切割下链，然后切割上链。I-TevI的这些特性被纳入一个模型中，在该模型中，内切酶通过一个灵活的铰链实现远距离切割。
