Bridges B A
MRC Cell Mutation Unit, University of Sussex, Falmer, Brighton, UK.
Mutat Res. 1993 Jul;302(3):173-6. doi: 10.1016/0165-7992(93)90045-w.
Escherichia coli WP2 trpE65(ochre), when grown to stationary phase and plated on glucose salts medium, gave rise to slow growing tryptophan-independent mutants which formed increasing numbers of visible colonies from about day 6 onwards. These mutants were neither revertants at the ochre codon nor mutants at the tRNA suppressor loci normally found in this strain with logarithmic phase mutagenesis. The yield of mutants was not affected by the presence of the following alleles, umuC122, lexA102, polA1, recA1, recA56 or del(srlR-recA)306, except that in the three recA-defective strains, mutant colonies were initially slower to appear, possibly reflecting a lower viability in the inoculum. Stationary-phase spontaneous mutation in bacteria carrying on ochre mutation is thus a distinct and specific process that does not require the SOS system, or UvrA protein or DNA polymerase I. It may reflect the occurrence of a type of non-bulky DNA damage with altered base pairing specificity. In 3 out of 4 experiments with a strain carrying recA441 plus lexA51(Def) the rate of stationary-phase mutagenesis was elevated suggesting that there may be an additional component requiring an activated SOS system.
大肠杆菌WP2 trpE65（赭石型）在生长至稳定期并接种于葡萄糖盐培养基上时，会产生生长缓慢的色氨酸非依赖型突变体，从大约第6天起，可见菌落数量不断增加。这些突变体既不是赭石密码子的回复突变体，也不是该菌株在对数期诱变时通常在tRNA抑制基因座发现的突变体。突变体的产量不受以下等位基因umuC122、lexA102、polA1、recA1、recA56或del(srlR-recA)306的影响，只是在三个recA缺陷型菌株中，突变菌落最初出现得较慢，这可能反映了接种物中较低的活力。因此，携带赭石突变的细菌中的稳定期自发突变是一个独特而特异的过程，不需要SOS系统、UvrA蛋白或DNA聚合酶I。它可能反映了一种碱基配对特异性改变的非大块DNA损伤的发生。在使用携带recA441加lexA51(Def)的菌株进行的4次实验中，有3次稳定期诱变率升高，这表明可能存在一个需要激活的SOS系统的额外成分。
