NEW PATHWAY FOR DNA-REPAIR IN ESCHERICHIA-COLI
NEW PATHWAY FOR DNA-REPAIR IN ESCHERICHIA-COLI
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DOI：
10.1038/267281a0
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发表时间：
1977-01-01
期刊：
影响因子：
64.8
通讯作者：
CAIRNS, J
中科院分区：
文献类型：
--
作者：
SAMSON, L;CAIRNS, J
大多数关于诱变的研究涉及将越来越多的细胞群体短期暴露于大剂量的诱变剂。然而，在自然环境中，细胞可能更频繁地长时间暴露于低浓度的诱变剂。因此，我们测量了在极低浓度诱变剂存在下连续生长的大肠杆菌细胞中突变体的积累。由于许多诱变剂非常不稳定，因此有必要设计一种系统，使细胞能够持续暴露于新鲜的诱变剂。为此，我们利用了某些细菌在附着在微孔过滤器底部时可以生长和分裂的事实。该系统最初由 Helmstetter 和 Cummings 开发，作为生产同步细胞的一种手段，因为当生长培养基通过过滤器时，它会带走每对新分裂细胞中未附着的子细胞。因此，待研究的诱变剂可以储存在稳定的条件下，并且仅在通过过滤器之前立即与生长培养基混合；例如，诱变剂 N-甲基-N'-硝基-硝基-异胍 (MNNG) 可以储存在 pH 5.0 的柠檬酸盐缓冲液中，其半衰期为 40 小时，而合成基本培养基中的半衰期为 2.3 小时2,3。我们打算确定各种诱变剂的环境浓度与所产生的突变率之间的关系。研究的第一个诱变剂是 MNNG，结果完全出乎意料。
MOST studies on mutagenesis involve exposing a growing population of cells to a large dose of mutagen for a short period. In a natural environment, however, cells are probably exposed more often to a low concentration of mutagens for long periods. We therefore measured the accumulation of mutants inEscherichia colicells growing continuously in the presence of very low concentrations of mutagens. Because many mutagens are highly unstable, it was necessary to devise a system in which cells could be continuously exposed to fresh mutagen. To do this we took advantage of the fact that certain bacteria can grow and divide while attached to the underside of a Millipore filter. This system was originally developed by Helmstetter and Cummings1as a means of producing synchronous cells, because as growth medium is passed through the filter it carries away with it the unattached daughter from each pair of newly divided cells. The mutagen to be studied can therefore be stored in stable conditions and only mixed with the growth medium immediately before being passed through the filter; for example the mutagenN-methyl-N′-nitro-nitro-soguanidine (MNNG) can be stored in citrate buffer atpH 5.0 in which it has a half life of 40 h compared with 2.3 h in synthetic minimal media2,3. We had intended to determine the relationship between ambient concentration of various mutagens and resulting mutation rate. The first mutagen studied was MNNG and the results were totally unexpected.