RecA是原核生物体内参与DNA同源识别过程的一种关键蛋白, 长期以来一直是同源重组相关课题的重要研究对象. 通过荧光显微示踪方法, 发现在同源识别过程中 RecA与单链DNA形成的核蛋白丝与模板DNA的结合是短时（τ=0.2 s）和短程（l=1.05 μm）的, 结合后搜寻模板DNA上的同源位点的过程可分为布朗运动和定向运动两种模式. 结合时核蛋白丝并不是缠绕在模板DNA上, 而是以一种更弱的方式结合在模板DNA外侧进行位点搜寻. 如果在该过程中没有找到同源位点, 核蛋白丝就会脱离模板DNA, 并寻找下一次与模板DNA结合的机会, 重复以上过程.%RecA plays an important role in homologous recognition in prokaryotes, and it has become a hot point in homologous recognition related research since its discovery. We establish an assay by combining total internal reflection fluorescence and flow stretching to visualize in real time the motion of single RecA-ssDNA filaments which are tagged with fluorescent beads. This enables us to study the interaction of RecA-ssDNA filaments with their templates in the homologous recognition process. It is found that the searching and binding is a short-time (τ=0.2 s) and short-distance (l=1.05 μm) process. Two distinguished motion modes for the RecA-ssDNA filament are observed, a Brownian motion and a directed motion. The observations suggest a model that a RecA-ssDNA filament just interacts weakly with the template DNA before it binds firmly to the template DNA. If no homologous site is found in a searching process, the filament drops off the template and repeats the searching process again until it finally finds its target.
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