Pato M L, Banerjee M
Department of Microbiology, University of Colorado Health Sciences Center, Denver 80262, USA.
Mol Microbiol. 2000 Aug;37(4):800-10. doi: 10.1046/j.1365-2958.2000.02042.x.
The Mu strong gyrase site (SGS), located in the centre of the Mu genome, is required for efficient Mu replication, as it promotes synapsis of the prophage termini. Other gyrase sites tested, even very strong ones, were unable to substitute for the SGS in Mu replication. To determine the features required for its unique properties, a deletion analysis was performed on the SGS. For this analysis, we defined the 20 bp centred on the midpoint of the 4 bp staggered cleavage made by gyrase to be the 'core' and the flanking sequences to be the 'arms'. The deletion analysis showed that (i) approximately 40 bp of the right arm is required, in addition to core sequences, for both efficient Mu replication and gyrase cleavage; and (ii) the left arm was not required for efficient Mu replication, although it was required for efficient gyrase cleavage. These observations implicated the right arm as the unique feature of the SGS. The second observation showed that strong gyrase cleavage and Mu replication could be dissociated and suggested that even weak gyrase sites, if supplied with the right arm of the SGS, could promote Mu replication. Hybrid sites were constructed with gyrase sites that could not support efficient Mu replication. The SGS right arm was used to replace one arm of the strong pSC101 gyrase site or the weaker pBR322 site. The pSC101 hybrid site allowed efficient Mu replication, whereas the pBR322 hybrid site allowed substantial, but reduced, replication. Hence, it appears that optimal Mu replication requires a central strong gyrase site with the properties imparted by the right arm sequences. Possible roles for the SGS right arm in Mu replication are addressed.
位于Mu基因组中心的Mu强解旋酶位点（SGS）对于Mu的高效复制是必需的，因为它能促进前噬菌体末端的联会。所测试的其他解旋酶位点，即使是很强的位点，也无法在Mu复制中替代SGS。为了确定其独特性质所需的特征，对SGS进行了缺失分析。在该分析中，我们将以解旋酶产生的4 bp交错切割中点为中心的20 bp定义为“核心”，侧翼序列定义为“臂”。缺失分析表明：（i）除核心序列外，右臂大约40 bp对于高效的Mu复制和解旋酶切割都是必需的；（ii）左臂对于高效的Mu复制不是必需的，尽管它对于高效的解旋酶切割是必需的。这些观察结果表明右臂是SGS的独特特征。第二项观察结果表明，强解旋酶切割和Mu复制可以分离，这表明即使是弱解旋酶位点，如果提供SGS的右臂，也可以促进Mu复制。用不能支持高效Mu复制的解旋酶位点构建了杂交位点。SGS右臂用于替换强pSC101解旋酶位点或较弱的pBR322位点的一个臂。pSC101杂交位点允许高效的Mu复制，而pBR322杂交位点允许大量但减少的复制。因此，看来最佳的Mu复制需要一个具有右臂序列赋予特性的中央强解旋酶位点。文中讨论了SGS右臂在Mu复制中的可能作用。
