Molecular Pathogenesis Program, Skirball Institute, New York University School of Medicine, 540 First Ave., New York, NY 10016, USA.
Plasmid. 2012 Mar;67(2):183-90. doi: 10.1016/j.plasmid.2012.01.006. Epub 2012 Jan 20.
The SaPIs and their relatives are phage satellites and are unique among the known bacterial pathogenicity islands in their ability to replicate autonomously. They possess a phage-like replicon, which is organized as two sets of iterons arrayed symmetrically to flank an AT-rich region that is driven to melt by the binding of a SaPI-specific initiator (Rep) to the flanking iterons. Extensive deletion analysis has revealed that Rep can bind to a single iteron, generating a simple shift in a gel mobility assay; when bound on both sides, a second retarded band is seen, suggesting independent binding. Binding to both sites of the ori is necessary but not sufficient to melt the AT-rich region and initiate replication. For these processes, virtually the entire origin must be present. Since SaPI replication can be initiated on linear DNA, it is suggested that bilateral binding may be necessary to constrain the intervening DNA to enable Rep-driven melting.
SaPIs 及其相关蛋白是噬菌体卫星，它们能够自主复制，这使它们在已知的细菌致病性岛中独具特色。它们拥有类似噬菌体的复制子，该复制子组织为两组交错排列的同向重复序列，两侧为富含 AT 的区域。SaPI 特异性启动子（Rep）与侧翼同向重复序列结合，可驱动富含 AT 的区域解链。大量缺失分析表明，Rep 可以结合单个同向重复序列，在凝胶迁移率分析中产生简单的移动变化；当结合在两侧时，会出现第二个迟滞带，表明独立结合。结合 ori 的两个位点是必需的，但不足以使富含 AT 的区域解链并启动复制。对于这些过程，实际上需要整个起始点。由于 SaPI 的复制可以在线性 DNA 上启动，因此推测双侧结合可能对于限制中间 DNA 使其能够被 Rep 驱动解链是必要的。
