Konforti B B, Davis R W
Department of Biochemistry, Stanford University School of Medicine, California 94305-5307.
J Biol Chem. 1990 Apr 25;265(12):6916-20.
The recA protein (RecA) promotes DNA pairing and strand exchange optimally in the presence of single-stranded binding protein (SSB). Under these conditions, 3' homologous ends are essential for stable joint molecule formation between linear single-stranded DNA (ssDNA) and supercoiled DNA (i.e. 3' ends are 50-60 times more reactive than 5' ends). Linear ssDNAs with homology at the 5' end do not participate in pairing. In the absence of SSB, the strand exchange reaction is less efficient; however, linear ssDNAs with 3' end homology are still 5- to 10-fold more reactive than those with 5' end homology. The preference for a 3' homologous end in the absence of SSB suggests that this is an intrinsic property of RecA-promoted strand exchange. The preferential reactivity of 3' homologous ends is likely to be a consequence of the polarity of polymerization of RecA on ssDNA. Specifically, since RecA polymerizes in the 5'----3' direction, 3' ends are more likely to be coated with RecA and, hence, will be more reactive than 5' ends.
在单链结合蛋白（SSB）存在的情况下，重组蛋白A（RecA）能最佳地促进DNA配对和链交换。在这些条件下，3'同源末端对于线性单链DNA（ssDNA）和超螺旋DNA之间稳定的连接分子形成至关重要（即3'末端的反应活性比5'末端高50 - 60倍）。5'末端具有同源性的线性ssDNA不参与配对。在没有SSB的情况下，链交换反应效率较低；然而，具有3'末端同源性的线性ssDNA的反应活性仍比具有5'末端同源性的线性ssDNA高5至10倍。在没有SSB时对3'同源末端的偏好表明这是RecA促进的链交换的固有特性。3'同源末端的优先反应活性可能是RecA在ssDNA上聚合极性的结果。具体而言，由于RecA沿5'----3'方向聚合，3'末端更有可能被RecA覆盖，因此比5'末端更具反应活性。
