DasGupta C, Radding C M
Proc Natl Acad Sci U S A. 1982 Feb;79(3):762-6. doi: 10.1073/pnas.79.3.762.
Escherichia coli recA protein makes joint molecules from single-stranded circular phage DNA (viral or plus strand) and homologous linear duplex DNA by a polar reaction that displaces the 5' end of the plus strand from the duplex molecule [Kahn, R., Cunningham, R. P., DasGupta, C. & Radding, C. M. (1981) Proc. Natl. Acad. Sci. USA 78, 4786-4790]. Growth of the heteroduplex joint, which results from strand exchange or branch migration, stopped at the borders of regions of nonhomologous DNA that were variously located 145, 630, or 1202 nucleotides from the end. Accumulation of migrating branches at heterologous borders demonstrates that their migration is not the result of random diffusion but is actively driven by recA protein. Growth of the heteroduplex joint was blocked even when a heterologous insertion was located in the single-stranded DNA, a case in which the flexible single-stranded region might conceivably fold out of the way under some condition. The recA protein did not make joint molecules from phage phi X174 and G4DNAs, which are 70% homologous, but did join phage fd and M13DNAs, which are 97% homologous. In the latter case, heteroduplex joints extended through regions containing isolated mismatched base pairs but stopped in a region where the fd and M13 sequences differ by an average of 1 base pair in 10. These results suggest that in genetic recombination the discrimination of perfect or near-perfect homology from a high degree of relatedness may be attributable in part to the mechanism by which recA protein promotes strand transfer.
大肠杆菌RecA蛋白通过一种极性反应，将单链环状噬菌体DNA（病毒链或正链）与同源线性双链DNA形成连接分子，该反应会使双链分子中正链的5'端被置换出来[卡恩，R.，坎宁安，R. P.，达斯古普塔，C. & 拉丁，C. M.（1981年）《美国国家科学院院刊》78卷，4786 - 4790页]。由链交换或分支迁移产生的异源双链连接的生长，在距离末端145、630或1202个核苷酸处不同位置的非同源DNA区域边界处停止。在异源边界处迁移分支的积累表明，它们的迁移不是随机扩散的结果，而是由RecA蛋白积极驱动的。即使异源插入位于单链DNA中，异源双链连接的生长也会受阻，在这种情况下，柔性单链区域在某些条件下可能会折叠避开。RecA蛋白不能使70%同源的噬菌体φX174和G4 DNA形成连接分子，但能连接97%同源的噬菌体fd和M13 DNA。在后一种情况下，异源双链连接延伸穿过包含孤立错配碱基对的区域，但在fd和M13序列平均每10个碱基对就有1个不同的区域停止。这些结果表明，在基因重组中，从高度相关性中区分完美或近乎完美的同源性，可能部分归因于RecA蛋白促进链转移的机制。
