Ward C B, Glaser D A
Proc Natl Acad Sci U S A. 1969 Jul;63(3):800-4. doi: 10.1073/pnas.63.3.800.
Synchronized cultures of rapidly growing E. coli B/r cells were starved for a required amino acid at various cell ages to allow ongoing chromosome replication to be completed without initiation of new replication cycles. It has been found that when such synchronized cultures are exposed to the mutagen nitrosoguanidine, genetic markers just in the process of replication show a markedly higher mutation rate than markers elsewhere on the chromosome. The number of growing points on the chromosome at each cell age can then be determined by observing the nitrosoguanidine-induced mutation rates for specific genetic markers on the genome. These experiments indicate that there exist multiple growing points on the genome for about ten minutes during the life cycle when the cells are growing with a doubling time of 28 minutes.
将快速生长的大肠杆菌B/r细胞同步培养，在不同细胞年龄使其缺乏一种必需氨基酸，以允许正在进行的染色体复制完成而不启动新的复制周期。已发现，当将这种同步培养物暴露于诱变剂亚硝基胍时，正在复制过程中的遗传标记显示出比染色体上其他位置的标记明显更高的突变率。然后，通过观察基因组上特定遗传标记的亚硝基胍诱导的突变率，可以确定每个细胞年龄时染色体上生长点的数量。这些实验表明，在细胞以28分钟的倍增时间生长的生命周期中，基因组上大约有十分钟存在多个生长点。
