Kim J I, Heuser J, Cox M M
Department of Biochemistry, University of Wisconsin, Madison 53706.
J Biol Chem. 1989 Dec 25;264(36):21848-56.
recA protein binding to duplex DNA is enhanced when a B form DNA substrate is replaced with a left-handed Z form helix. This represents a kinetic rather than an equilibrium effect. Binding to Z DNA is much faster than binding to B DNA. In other respects, binding to the two DNA forms is quite similar. recA protein binds to B or Z DNA with a stoichiometry of 1 monomer/4 base pairs. The final protein filament exhibits a right-handed helical structure when either B or Z form DNAs are bound. There are only two evident differences: the kcat for ATP hydrolysis is reduced 3-4-fold when Z DNA is bound, and recA binding at equilibrium is less stable on Z DNA than on B DNA. At steady state, the binding favors B DNA in competition experiments. The results indicate that Z DNA binding by recA protein follows the same pathway as for recA binding to B DNA, but that the nucleation step is faster on the Z form helix.
当B型DNA底物被左手螺旋的Z型螺旋取代时，recA蛋白与双链DNA的结合会增强。这代表的是一种动力学效应而非平衡效应。与Z型DNA的结合比与B型DNA的结合要快得多。在其他方面，与这两种DNA形式的结合非常相似。recA蛋白以1个单体/4个碱基对的化学计量比与B型或Z型DNA结合。当结合B型或Z型DNA时，最终的蛋白丝呈现右手螺旋结构。只有两个明显的差异：当结合Z型DNA时，ATP水解的催化常数降低了3至4倍，并且在平衡状态下，recA在Z型DNA上的结合稳定性低于在B型DNA上的结合稳定性。在竞争实验的稳态下，结合更倾向于B型DNA。结果表明，recA蛋白与Z型DNA的结合遵循与recA与B型DNA结合相同的途径，但在Z型螺旋上成核步骤更快。
