Blake J A, Ganguly N, Sherratt D J
Biomedical Research Centre, Ninewells Hospital, Dundee, UK.
Mol Microbiol. 1997 Jan;23(2):387-98. doi: 10.1046/j.1365-2958.1997.2261600.x.
Xer site-specific recombination functions in the stable inheritance of circular plasmids and bacterial chromosomes. Two related recombinases, XerC and XerD, mediate this recombination, which 'undoes' the potential damage of homologous recombination. Xer recombination on natural plasmid sites is preferentially intramolecular, converting plasmid multimers to monomers. In contrast, recombination at the Escherichia coli recombination site, dif, occurs both intermolecularly and intramolecularly, at least when dif is inserted into a multicopy plasmid. Here the DNA sequence features of a family of core recombination sites in which the XerC- and XerD-binding sites, which are separated by 6 bp, were analysed in order to ascertain what determines whether recombination will be preferentially intramolecular, or will occur both within and between molecules. Sequence changes in either the XerC- or XerD-binding site can alter the recombination outcome. Preferential intramolecular recombination between a pair of recombination sites requires additional accessory DNA sequences and accessory recombination proteins and is correlated with reduced affinities of recombinase binding to recombination core sites, reduced XerC-mediated cleavage in vitro, and an apparent increased overall bending in recombinase-core-site complexes.
Xer位点特异性重组在环状质粒和细菌染色体的稳定遗传中发挥作用。两种相关的重组酶XerC和XerD介导这种重组，它“消除”了同源重组的潜在损害。天然质粒位点上的Xer重组优先发生在分子内，将质粒多聚体转化为单体。相比之下，大肠杆菌重组位点dif处的重组在分子间和分子内都会发生，至少当dif插入多拷贝质粒时是这样。在此，对一个核心重组位点家族的DNA序列特征进行了分析，其中XerC和XerD结合位点被6个碱基对隔开，以确定是什么决定了重组是优先发生在分子内，还是会在分子内和分子间都发生。XerC或XerD结合位点的序列变化都可以改变重组结果。一对重组位点之间优先发生分子内重组需要额外的辅助DNA序列和辅助重组蛋白，并且与重组酶与重组核心位点的结合亲和力降低、体外XerC介导的切割减少以及重组酶-核心位点复合物中明显增加的整体弯曲相关。
