ANALYSIS OF STRAND EXCHANGE AND DNA-BINDING OF ENHANCER-INDEPENDENT GIN RECOMBINASE MUTANTS
ANALYSIS OF STRAND EXCHANGE AND DNA-BINDING OF ENHANCER-INDEPENDENT GIN RECOMBINASE MUTANTS
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DOI：
10.1002/j.1460-2075.1993.tb05746.x
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发表时间：
1993-03-01
期刊：
影响因子：
11.4
通讯作者：
COZZARELLI, NR
中科院分区：
文献类型：
--
作者：
KLIPPEL, A;KANAAR, R;COZZARELLI, NR
噬菌体Mu的Gin重组系统介导DNA序列在两个位点之间的倒置(GIX)。除了Gin蛋白和GIX位点外，重组还需要一个由宿主因子FIS结合的增强子。我们分析了Gin的突变体，在没有增强子和FIS的情况下发挥作用，除了倒位外，还介导了缺失和分子间融合。倒位引起的连接数变化表明，突变体Gin单独可以形成相同的突触复合体，并可以使用与完整的野生型系统相同的链交换机制。然而，连接数的变化也表明，与野生型Gin不同，突变体Gin可以通过多个突触复合体进行重组，并且可以在没有突触的情况下放松DNA。这一扩展的谱系允许突变的Gin介导野生型Gin不执行的DNA重排。因为突变体Gin，而不是野生型Gin，在结合时解开GIX位点DNA，我们假设FIS和增强子通过(-)超级卷曲来促进与野生型Gin的这种解离。对DNA融合过程中的拓扑变化的分析表明，GIX位点的平行构型和野生型Gin交换过程中位点的右旋都是底物的(-)超螺旋和突触复合体中包裹的超螺旋数量的结果。
The Gin recombination system of phage Mu mediates inversion of the DNA sequence between two sites (gix). In addition to Gin protein and gix sites, recombination requires an enhancer bound by the host factor FIS. We analyzed mutants of Gin that function in the absence of the enhancer and FIS and mediate deletion and intermolecular fusion in addition to inversion. The linking number changes caused by inversion imply that,mutant Gin alone can form the same synaptic complex and can use the same strand exchange mechanism as the complete wild-type system. However, the linking number changes also reveal that unlike wild-type Gin, mutant Gin can recombine through more than one synaptic complex and can relax DNA in the absence of synapsis. This expanded repertoire allows mutant Gin to mediate DNA rearrangements not performed by wild-type Gin. Because mutant Gin, but not wild-type Gin, unwinds gix site DNA upon binding, we postulate that FIS and the enhancer function with (-) supercoiling to promote this unwinding with wild-type Gin. The analysis of the topological changes during DNA fusion shows that both the parallel gix site configuration and the right-handed rotation of the sites during exchange of wild-type Gin are a result of the (-) supercoiling of the substrate and the number of entrapped supercoils in the synaptic complex.