Engberg B, Nordström K
J Bacteriol. 1975 Jul;123(1):179-86. doi: 10.1128/jb.123.1.179-186.1975.
The R-factor R1drd-19 mediates resistance to beta-lactam antibiotics via a beta-lactamase. A strain of Escherichia coli K-12 carrying R1drd-19 was grown at different growth rates by using different carbon sources. The specific rate of production of the R1 beta-lactamase increased linearly with the growth rate and with the gene dosage. The content of R1 deoxyribonucleic acid was estimated by alkaline sucrose gradient centrifugation and by analysis of the specific rate of beta-lactamase synthesis in nutritional shift-up experiments and was found to decrease fivefold when the growth rate was increased from 0.4 to 1.8 doublings per h. The number of R1 molecules per cell decreased from six to two in the same growth range. The presence of the plasmid affected the mean cell size significantly; at a growth rate of 0.4 doublings per h the R-+ cells were on the average 50% bigger than the R-minus cells, whereas the effect was less than 10% at a growth rate of 1.8 doublings per h. Several reports in the leterature state that the initiation mass of chromosome replication is constant. In this paper it is shown that the initiation mass of R1 replication is proportional to the growth rate. Thus, the replication of the plasmid R1 and of the chromosome are independently regulated processes. It is argued that plasmid replication is under negative control.
R 因子 R1drd - 19 通过一种β - 内酰胺酶介导对β - 内酰胺类抗生素的抗性。利用不同碳源使携带 R1drd - 19 的大肠杆菌 K - 12 菌株以不同生长速率生长。R1β - 内酰胺酶的比产生速率随生长速率和基因剂量呈线性增加。通过碱性蔗糖梯度离心以及在营养上调实验中分析β - 内酰胺酶合成的比速率来估算 R1 脱氧核糖核酸的含量，结果发现当生长速率从每小时 0.4 代增加到 1.8 代时，其含量降低了五倍。在相同生长范围内，每个细胞中 R1 分子的数量从六个减少到两个。该质粒的存在显著影响平均细胞大小；在每小时 0.4 代的生长速率下，R⁺细胞平均比 R⁻细胞大 50%，而在每小时 1.8 代的生长速率下，这种影响小于 10%。文献中有几篇报道称染色体复制的起始质量是恒定的。本文表明 R1 复制的起始质量与生长速率成正比。因此，质粒 R1 和染色体的复制是独立调控的过程。有人认为质粒复制受到负调控。
