Pato M L
Department of Microbiology, University of Colorado Health Sciences Center, Denver 80262.
Proc Natl Acad Sci U S A. 1994 Jul 19;91(15):7056-60. doi: 10.1073/pnas.91.15.7056.
The bacteriophage Mu genome contains a strong DNA gyrase binding site (SGS) near its center, and disruption of the SGS by deletion or by insertion results in long delays in replication following induction of the appropriate lysogen. To determine if the central location of the SGS is obligatory for its function in Mu replication, we pursued two lines of investigation. First, fragments of Mu DNA containing the SGS were inserted into various locations in a Mu prophage lacking the central SGS. Replication following induction was restored in all of the lysogens constructed, but the observed rate of replication for different prophages decreased with increasing distance between the new location of the SGS and the center of the genome. We also deleted different lengths of DNA from within the right half of a wild-type prophage, retaining the SGS and displacing it from a central location. Replication rates of the deleted prophages were reduced, with larger deletions resulting in larger reductions. Pairing deletions in the right half of the prophage with a deletion in the left half resulted in substantially higher rates of replication than observed with the right half deletions alone. We conclude that the SGS must be located centrally between the Mu termini for optimal rates of Mu replication. These results are discussed in terms of a model that proposes that the SGS is involved in organizing the topology of supercoiled prophage DNA to assist in synapsis of the Mu termini.
噬菌体Mu基因组在其中心附近含有一个强DNA回旋酶结合位点（SGS），通过缺失或插入破坏该SGS会导致诱导相应溶原菌后复制出现长时间延迟。为了确定SGS的中心位置对其在Mu复制中的功能是否必不可少，我们进行了两条研究路线。首先，将含有SGS的Mu DNA片段插入缺乏中心SGS的Mu原噬菌体的不同位置。在构建的所有溶原菌中，诱导后的复制得以恢复，但不同原噬菌体观察到的复制速率随着SGS的新位置与基因组中心之间距离的增加而降低。我们还从野生型原噬菌体右半部分内部删除了不同长度的DNA，保留SGS并将其从中心位置移位。缺失的原噬菌体的复制速率降低，缺失越大，降低幅度越大。将原噬菌体右半部分的缺失与左半部分的缺失配对，导致复制速率比仅观察到右半部分缺失时显著更高。我们得出结论，SGS必须位于Mu末端之间的中心位置，以实现Mu复制的最佳速率。根据一个模型对这些结果进行了讨论，该模型提出SGS参与组织超螺旋原噬菌体DNA的拓扑结构，以协助Mu末端的联会。
