The basis of asymmetry in IS2 transposition.
The basis of asymmetry in IS2 transposition.
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IS2 转座不对称的基础。
DOI：
10.1046/j.1365-2958.2001.02662.x
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发表时间：
2001
影响因子：
3.6
通讯作者：
Grindley,ND
中科院分区：
文献类型：
--
作者：
Lewis,LA;Gadura,N;Greene,M;Saby,R;Grindley,ND
IS2转座的第一步，即IS2小环的形成，IS两端的作用不同。末端切割仅在右侧反向重复序列 (IRR)（供体末端）处启动，而 IRL 始终是目标。在所得的小环连接处，两个邻接末端被 1 或 2 个碱基对的间隔区分开。在这项研究中，我们确定了供体和靶标功能的决定因素。 IRL 无法充当供体，很大程度上是由于 IRL 和 IRR 之间的两个序列差异所致——保守转座酶结合序列和元件末端之间的额外碱基对，以及末端二核苷酸从 CA-3' 变为 TA-3'。这两个变化也对小圆形结间隔物施加了特征尺寸。 IRL 有效目标功能所需的唯一序列似乎包含在位置 11-42 的片段内。尽管 IRR 可以作为靶标，但其较短的长度以及与转座酶（位置 1-7）的额外接触导致小环具有较长且不合适的间隔区。我们提出了一个突触复合体模型，其中 IRL 末端与转座酶在初始和最终链转移步骤中进行不同的接触。 IRR 和 IRL 之间的序列差异以及由此产生的 IRL 行为特征可能是经过选择的，因为它们优化了来自小环连接启动子 Pjunc 的转座酶的表达。
In the first step of IS2transposition, the formation of an IS2minicircle, the roles of the two IS ends differ. Terminal cleavage initiates exclusively at the right inverted repeat (IRR) – the donor end – whereas IRL is always the target. At the resulting minicircle junction, the two abutted ends are separated by a spacer of 1 or 2 basepairs. In this study, we have identified the determinants of donor and target function. The inability of IRL to act as a donor results largely from two sequence differences between IRL and IRR – an extra basepair between the conserved transposase binding sequences and the end of the element, and a change of the terminal dinucleotide from CA‐3′ to TA‐3′. These two changes also impose a characteristic size on the minicircle junction spacer. The only sequences required for the efficient target function of IRL appear to be contained within the segment from position 11–42. Although IRR can function as a target, its shorter length and additional contacts with transposase (positions 1–7) result in minicircles with longer, and inappropriate, spacers. We propose a model for the synaptic complex in which the terminus of IRL makes different contacts with the transposase for the initial and final strand transfer steps. The sequence differences between IRR and IRL, and the behavioural characteristics of IRL that result from them, have probably been selected because they optimize expression of transposase from the minicircle junction promoter, Pjunc.