Pato M L, Banerjee M
Department of Microbiology, University of Colorado Health Sciences Centre, Denver 80262, USA.
Mol Microbiol. 1996 Oct;22(2):283-92. doi: 10.1046/j.1365-2958.1996.00115.x.
A strong DNA gyrase-binding site (SGS) is located midway between the termini of the bacteriophage Mu genome and is required for efficient replicative transposition. We have proposed that the SGS promotes the efficient synapsis of the Mu prophage ends (an obligate early step in replicative transposition), and that it does so by helping to organize the prophage DNA into a supercoiled loop with the SGS at the apex of the loop and the prophage termini at the base. The positioning of the synapsing termini equidistant from the SGS is a key element in the proposed model. To test this proposal, we have constructed prophages with a second, internal right end and asked whether the natural, external right end or the internal right end is used for synapsis with the left end in the presence and absence of the SGS. In the presence of the central SGS, the natural, or outside, right end was used exclusively and very efficiently. In the absence of the central SGS, the internal right end was used preferentially and inefficiently: the efficiency of transposition decreased with increasing distance between the internal right end and the left end. Repositioning the SGS midway between the left end and an internal right end allowed highly efficient use of the internal right end. These results support a model in which gyrase can influence long-range DNA interactions to promote efficient synapsis of Mu prophage ends.
一个强DNA促旋酶结合位点（SGS）位于噬菌体Mu基因组两端之间的中间位置，是高效复制转座所必需的。我们提出，SGS促进Mu原噬菌体末端的有效联会（复制转座中一个必不可少的早期步骤），其作用方式是帮助将原噬菌体DNA组织成一个超螺旋环，SGS位于环的顶端，原噬菌体末端位于环的底部。在提出的模型中，联会末端与SGS等距定位是一个关键要素。为了验证这一设想，我们构建了带有第二个内部右端的原噬菌体，并研究在有和没有SGS的情况下，是天然的外部右端还是内部右端用于与左端联会。在存在中央SGS的情况下，天然的或外部的右端被专门且高效地使用。在没有中央SGS的情况下，内部右端被优先且低效地使用：转座效率随着内部右端与左端之间距离的增加而降低。将SGS重新定位到左端和一个内部右端之间的中间位置，可实现对内部右端的高效利用。这些结果支持了一个模型，即促旋酶可以影响远距离DNA相互作用，以促进Mu原噬菌体末端的有效联会。
