Microbial Genetics Laboratory, Genetic Strains Research Center, National Institute of Genetics 1111, Yata, Mishima, Shizuoka 411-8540, Japan.
Microbial Genetics Laboratory, Genetic Strains Research Center, National Institute of Genetics 1111, Yata, Mishima, Shizuoka 411-8540, Japan; Department of Genetics, SOKENDAI (The Graduate University for Advanced Studies) 1111, Yata, Mishima, Shizuoka 411-8540, Japan.
Cell Rep. 2017 Oct 31;21(5):1347-1360. doi: 10.1016/j.celrep.2017.10.014.
Condensins load onto DNA to organize chromosomes. Smc-ScpAB clearly loads onto the parS sites bound by Spo0J, but other loading site(s) must operate independently of parS. In this study, we asked where and how Smc-ScpAB normally selects its loading site. Our results suggest that rDNA is also a loading site. A pull-down assay revealed that Smc-ScpAB preferentially loads onto rDNA in the wild-type cell and even in a Δspo0J mutant but not in a Δsmc mutant. Moreover, we showed that deletion mutants of rDNAs cause a defect in nucleoid separation, and at least two rDNAs near oriC are essential for separation. Full-length rDNA, including promoters, is required for loading and nucleoid separation. A synthetic defect by deletions of both rDNA and spo0J resulted in more aberrant nucleoid separation. We propose that a single-stranded segment of DNA that is exposed at highly transcribed rRNA operons would become a target for Smc-ScpAB loading.
凝聚素加载到 DNA 上以组织染色体。 Smc-ScpAB 显然加载到 Spo0J 结合的 parS 位点上，但其他加载位点必须独立于 parS 运作。在这项研究中，我们询问 Smc-ScpAB 通常如何选择其加载位点。我们的结果表明 rDNA 也是一个加载位点。下拉测定显示， Smc-ScpAB 在野生型细胞中优先加载到 rDNA 上，即使在Δspo0J 突变体中也是如此，但在Δsmc 突变体中则不然。此外，我们表明 rDNA 的缺失突变体会导致核体分离缺陷，至少两个位于 oriC 附近的 rDNA 对于分离是必需的。全长 rDNA，包括启动子，是加载和核体分离所必需的。 rDNA 和 spo0J 的缺失都会导致更异常的核体分离。我们提出，在高度转录的 rRNA 操纵子中暴露的单链 DNA 片段将成为 Smc-ScpAB 加载的目标。
