Li Z, Karakousis G, Chiu S K, Reddy G, Radding C M
Department of Genetics, Yale University School of Medicine, New Haven, CT 06510, USA.
J Mol Biol. 1998 Mar 6;276(4):733-44. doi: 10.1006/jmbi.1997.1572.
Bacteriophage lambda encodes a 28 kDa protein called beta that binds to single-stranded DNA and promotes the renaturation of complementary single strands. beta Protein fails to bind directly to duplex DNA but remains bound to the DNA product of renaturation that beta itself catalyzes. These observations led to an examination of the ability of beta protein to promote strand exchange. beta Protein caused the replacement of a 43-mer oligonucleotide annealed to M13 circular single-stranded DNA by a homologous 63-mer whose 20 extra nucleotide residues were complementary to the adjacent 3' region of M13 DNA. The role of beta protein in this reaction was manifested in several ways: beta protein pushed the exchange through four to eight mismatches, which blocked exchange mediated by spontaneous renaturation and branch migration; beta imposed a polarity on the strand exchange that was lacking in the spontaneous reaction; and beta remained bound to the heteroduplex product of strand exchange. These observations reveal a mechanism by which a protein can drive strand exchange in one direction without using ATP or any other exogenous source of energy.
λ噬菌体编码一种名为β的28 kDa蛋白质，它能与单链DNA结合并促进互补单链的复性。β蛋白不能直接与双链DNA结合，但会一直结合在由其自身催化复性产生的DNA产物上。这些观察结果促使人们对β蛋白促进链交换的能力进行研究。β蛋白导致一段与M13环状单链DNA退火的43聚体寡核苷酸被一段同源的63聚体取代，该63聚体额外的20个核苷酸残基与M13 DNA相邻的3'区域互补。β蛋白在该反应中的作用体现在几个方面：β蛋白推动交换通过4到8个错配，这些错配会阻碍由自发复性和分支迁移介导的交换；β在链交换中施加了一种自发反应中不存在的极性；并且β会一直结合在链交换产生的异源双链产物上。这些观察结果揭示了一种机制，通过该机制一种蛋白质可以在不使用ATP或任何其他外源能量来源的情况下驱动链交换向一个方向进行。
