Initiation and velocity of chromosome replication in Escherichia coli B/r and K-12
Initiation and velocity of chromosome replication in Escherichia coli B/r and K-12
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DOI：
10.1128/jb.180.2.265-273.1998
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发表时间：
1998-01-01
影响因子：
3.2
通讯作者：
Bremer, H
中科院分区：
文献类型：
--
作者：
Bipatnath, M;Dennis, PP;Bremer, H
在两种常见的大肠杆菌菌株 Bir 和 K-12 AB1157 中，在一系列指数生长速率下检查了影响染色体复制的大分子组成和许多参数。基于用利福平处理指数培养物后改进的 DNA 测量，确定了每个染色体复制起点的细胞质量（起始质量）以及染色体从起点复制到终点所需的时间（C 期）。对于这两种菌株，起始质量分别接近每 oriC 培养物质量的 8 x 10(-10) 和 10 x 10(-10) 光密度单位（460 nm），生长速率高于 1 倍/小时（37 摄氏度）。对于 AB1157，每个 oriC 的蛋白质含量随着生长速率的增加而减少，而对于 B/r 菌株则几乎保持恒定。两种菌株的C期以基本相同的方式从0.6倍增/小时的约70分钟减少到3倍增/小时的约33分钟。根据起始质量和 C 周期，可以准确确定具有已知图谱位置的基因在不同生长速率下的相对或绝对拷贝数。当生长速度超过 2 倍/小时时，当染色体高度分支时，靠近起点的基因比靠近终点的基因普遍性高出三倍左右。在0.6倍增/小时的生长速度下，该比率仅为1.7左右，这反映了染色体分支程度较低。
The macromolecular composition and a number of parameters affecting chromosome replication were examined over a range of exponential growth rates in two common Escherichia coli strains, Bir and K-12 AB1157. Based on improved measurements of DNA after treatment of exponential cultures with rifampin, the cell mass per chromosomal replication origin (initiation mass) and the time required to replicate the chromosome from origin to terminus (C period) were determined. For these two strains, the initiation mass approached values of 8 x 10(-10) and 10 x 10(-10) units of optical density (at 460 nm) of culture mass per oriC, respectively, at growth rates above 1 doubling/h (at 37 degrees C). The amount of protein per oriC decreased with increasing growth rate for AB1157 and remained nearly constant for the B/r strain. The C period decreased for both strains in an essentially identical manner from about 70 min at 0.6 doublings/h to about 33 min at 3 doublings/h. From the initiation mass and C period, relative or absolute copy numbers for genes with known map locations can be accurately determined at different growth rates. At growth rates above 2 doublings/h, when chromosomes are highly branched, genes near the origin are about threefold more prevalent than genes near the terminus. At a growth rate of 0.6 doubling/h, this ratio is only about 1.7, which reflects the lower degree of chromosome branching.