Structure And Stabilization Of The Bacterial Nucleoid

大肠杆菌的基因组DNA定位在一个或几个紧密的类核中。在快速生长的细胞中，类核呈现复杂的形状；这些形状与DNA的潜在排列的关系是结构上的兴趣，在基因定位和类核分割研究中具有潜在的重要性。为了帮助评估这种形状的变化，在细胞在溶液中重新定向时，通过DNA荧光显微镜或光学切片获得了单个类核的有限三维信息。这些技术也适用于肿胀细胞或球质体中增大的类核。所得到的图像表明，大部分明显的变化是由于从不同的方向和不同的焦平面成像更规则的底层类核形状。细胞暴露于氯霉素或嘌呤霉素后，类核图像可转化为紧凑的双核形状，与先前存在的双核结构一致。在固定相细胞中分离的类核和类核也呈现出双重形状，支持这种结构。潜在的结构被认为是两个亚基，对应于新生的子染色体，由间隔连接。亚基和间隔体似乎都在变形，以适应细胞或球质体内部的可用空间（“柔性双重态”模型）。

The genomic DNA of Escherichia coli is localized in one or a few compact nucleoids. Nucleoids in rapidly grown cells appear in complex shapes; the relationship of these shapes to underlying arrangements of the DNA is of structural interest and of potential importance in gene localization and nucleoid partition studies. To help assess this variation in shape, limited three-dimensional information on individual nucleoids was obtained by DNA fluorescence microscopy of cells as they reoriented in solution, or by optical sectioning. These techniques were also applied to enlarged nucleoids within swollen cells or spheroplasts. The resulting images indicated that much of the apparent variation was due to imaging from different directions and at different focal planes of more regular underlying nucleoid shapes. Nucleoid images could be transformed into compact doublet-shapes by exposure of cells to chloramphenicol or puromycin, consistent with a preexisting bipartite nucleoid structure. Isolated nucleoids and nucleoids in stationary phase cells also assumed a doublet shape, supporting such a structure. The underlying structure is suggested to be two subunits, corresponding to the nascent daughter chromosomes, joined by a spacer. Both the subunits and the spacer appear to deform to accommodate the space available within cells or spheroplasts ("flexible doublet" model).