Gauss G H, Lieber M R
Department of Pathology, Stanford University School of Medicine, California 94305-5324.
Genes Dev. 1992 Aug;6(8):1553-61. doi: 10.1101/gad.6.8.1553.
V(D)J recombination between recognition sites in the genome is characterized by certain biases. At some loci, proximal sites undergo recombination substantially more frequently than distal ones. The joining of DH/JH is an example of this. Because the DH element bears signal sequences on each side, inversion would be expected as often as deletion in DH/JH recombination. However, the markedly favored outcome is deletion, entailing utilization of the closer recombination site. One model proposed to explain these biases is the tracking model in which the recombinase tracks from one site to the other. Here, we have directly tested for various types of tracking in V(D)J recombination and have found no indication that it occurs. In addition, we have created DH-JH minilocus substrates for analysis of the basis for the preference for deletion. We find that we can reproduce the deletional bias for the system. Moreover, by flipping the orientation of the D segment, we can reverse the bias such that the frequency of inversions can exceed the number of deletions. These results indicate (1) that there is no intrinsic topological preference in this reaction, and (2) that the sequence of the signal and coding ends determines the bias.
基因组中识别位点之间的V(D)J重组具有某些偏向性。在一些基因座上，近端位点发生重组的频率明显高于远端位点。DH/JH的连接就是一个例子。由于DH元件两侧都带有信号序列，在DH/JH重组中，倒位预期会和缺失一样频繁。然而，明显更倾向的结果是缺失，这需要利用更近的重组位点。为解释这些偏向性而提出的一个模型是追踪模型，即重组酶从一个位点追踪到另一个位点。在这里，我们直接测试了V(D)J重组中各种类型的追踪，未发现其发生的迹象。此外，我们构建了DH-JH微基因座底物，用于分析缺失偏好的基础。我们发现我们能够重现该系统的缺失偏向性。而且，通过翻转D片段的方向，我们可以逆转这种偏向性，使得倒位频率能够超过缺失的数量。这些结果表明：（1）该反应不存在内在的拓扑学偏好；（2）信号末端和编码末端的序列决定了这种偏向性。
