步骤一: 交联: 加入甲醛可以使 DNA 与蛋白或蛋白与蛋白之间相互粘结, 这样会导致相互作用的 DNA 片段被交联在一起. (for example cis located promoters to trans located promoters, reveals interactions like the interaction between H enhancer and odorant receptor promoters).
步骤二: 限制酶消化: 加入过量限制性内切酶将未交联的 DNA 与交联的 DNA 相互分离. 限制酶的选择取决于需要分析的基因座位的情况. 限制序列较短 (4 bp) 的内切酶切点密集, 用于研究较短的座位 (< 10~20 kb), 而限制序列较长 (6 bp) 的内切酶用于研究较长的座位.
步骤三: 分子内连接:
在使用低剂量 DNA 底物的情况下, DNA 末端链接反应更偏好于将临近的 DNA 片段连接而非随机进行连接. 这种情况下, 两类连接反应会更频繁出现: 其一是限制酶未完全消化的 DNA 切口被重新连接, 这种情况大致占全部接口的 20% 到 30%, 此类连接与染色质构象捕获实验无关, 我们可以通过降低第一步交联反应的紧密程度来减少这类反应; 另一类频繁发生的连接反应是同一分子内的 DNA 的末端由于距离较近被连接, 这样的接口占到了全部接口的 30% 左右, 这类连接也会发生在交联后形成的蛋白与 DNA 复合物中不同 DNA 链之间 (图中展示的连接为复合物中相同来源 (红色) 的 DNA 末端被连接, 此外不同来源的 DNA 也可能被连接 (红色与蓝色之间). [19]
步骤四: 去交联: 步骤一中的交联可以通过高温去除, 所得到的 DNA 将在其序列两端与当中含有限制酶识别序列, 将这些 DNA 建成文库 (3C 库).
步骤五: 定量: 使用连接位点两端的引物进行聚合酶链式反应, 其结果可以半定量的表示 DNA 片段之间的相互作用. Quantitative PCR using Taqman probes (3C-qPCR) provides a more quantitative measurement of the fragment of interest. The Taqman probe and a constant primer hybridize to the restriction fragment that contains the site of contact and one test primer is designed against each neighboring restriction fragments. Together the probe and primers allow for a specific fluorescent signal to be emitted during amplification.[20]
3C方法已经证明调控元件与其调控的基因在空间上接近的重要性。例如,在表达球蛋白基因的组织中,β-球蛋白基因座控制区与这些基因形成环。在没有表达基因的组织中没有发现该环。[21] 这项技术进一步帮助了模式生物和人类染色体的遗传和[表观遗传学]研究。Template:Citation needed lead
Bailey等人已经鉴定了启动子区域中的ZNF143基序提供了启动子 - 增强子相互作用的序列特异性[46]. Mutation of ZNF143 motif decreased the frequency of promoter-enhancer interactions suggesting that ZNF143 is a novel chromatin-looping factor.
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