DNA relaxation-dependent phase biasing of the fim genetic switch in Escherichia coli depends on the interplay of H-NS, IHF and LRP
DNA relaxation-dependent phase biasing of the fim genetic switch in Escherichia coli depends on the interplay of H-NS, IHF and LRP
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DOI：
10.1111/j.1365-2958.2009.06919.x
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发表时间：
2009-12-01
影响因子：
3.6
通讯作者：
Dorman, Charles J.
中科院分区：
文献类型：
--
作者：
Corcoran, Colin P.;Dorman, Charles J.
DNA元件fimS的可逆倒位负责大肠杆菌1型菌毛的时相可变表达。FimB酪氨酸整合酶位点特异性重组酶以近似相等的效率在开-关和关-开方向上反转fimS。然而，当DNA超螺旋被放松时，fimS主要采用on方向。已知这种取向偏差需要fimS内的核苷酸相关蛋白LRP的结合。在这里，我们表明，结合IHF蛋白的一个网站紧邻fimS也需要相位上的取向偏差。在缺乏LRP和IHF结合的情况下，fimS采用关闭取向，并且需要H-NS蛋白来维持这种替代取向偏差。因此，fimS具有三个方向性因子，H-NS、IHF和LRP。相关的H-NS结合位点横跨在相关闭fimS中的左侧反向重复序列，并且当fimS反转到开启方向时，该位点被破坏。fimS的倒位以及DNA倒位偏置所需的H-NS结合位点的相关产生和去除代表了调节H-NS与DNA靶点相互作用以及影响位点特异性重组反应的新机制。
P>Reversible inversion of the DNA element fimS is responsible for the phase variable expression of type 1 fimbriae in Escherichia coli. The FimB tyrosine integrase site-specific recombinase inverts fimS in the on-to-off and off-to-on directions with approximately equal efficiencies. However, when DNA supercoiling is relaxed, fimS adopts predominantly the on orientation. This orientational bias is known to require binding of the nucleoid-associated protein LRP within fimS. Here we show that binding of the IHF protein to a site immediately adjacent to fimS is also required for phase-on orientational bias. In the absence of both LRP and IHF binding, fimS adopts the off orientation and the H-NS protein is required to maintain this alternative orientational bias. Thus, fimS has three Recombination Directionality Factors, H-NS, IHF and LRP. The relevant H-NS binding site straddles the left inverted repeat in phase-off fimS and this site is disrupted when fimS inverts to the on orientation. The inversion of fimS with the associated creation and removal of an H-NS binding site required for DNA inversion biasing represents a novel mechanism for modulating the interaction of H-NS with a DNA target and for influencing a site-specific recombination reaction.