Kopsidas G, MacPhee D G
Department of Microbiology, La Trobe University, Bundoora, Vic., Australia.
Mutat Res. 1994 Apr 15;306(2):111-7. doi: 10.1016/0027-5107(94)90021-3.
Reversion of the hisC3076 frameshift marker of Salmonella typhimurium has been measured following treatment of cells in growth and non-growth media with 9-aminoacridine (9AA). By varying the carbon source present in a defined medium, it has been shown that mutagenesis is reduced close to the spontaneous level in the presence of glucose whilst significant reductions are also observed with glucosamine, mannose, mannitol, fructose or glucose 6-phosphate. Intermediate mutant yields are observed when lactic acid or glycerol are present, whereas any one of a further group of carbon sources (gluconate, arabinose, ribose, succinate or casein hydrolysate) permit relatively large numbers of mutants to be recovered. Interestingly, when any one of these "high yield" carbon sources is supplemented with glucose the strong inhibitory effect characteristic of glucose is again observed. On the basis of these results, it can be concluded that inhibition of 9AA-induced reversion by a carbon source is not an exclusive property of glucose, although when more than one carbon source is present the inhibitory effect of glucose predominates. Possible explanations for these findings include the active exclusion of 9AA from cells as a direct consequence of glucose transport across the cell membrane. To address this possibility, cells were pre-grown in verapamil, a calcium channel antagonist which is known to increase the mutagenicity of various 9-anilinoacridine derivatives in S. typhimurium. We found that glucose inhibition of 9AA-induced mutagenesis was not relaxed to any significant extent following treatment with verapamil. In a further experiment, two glucose analogues (2'-deoxyglucose and methyl-D-glucoside) known to be actively transported into the cell but not metabolised past the first phosphorylation step were used. These analogues inhibit the transport into the cell of several types of molecules, but since they do not significantly depress 9AA mutagenesis it seems unlikely that blockage of 9AA transport across the cell membrane can be invoked to explain the inhibitory effect of glucose on 9AA mutagenesis. An alternative explanation based on glucose-mediated repression of an error-prone, mutation-generating, DNA-repair process is presented.
用9 - 氨基吖啶（9AA）处理生长和非生长培养基中的鼠伤寒沙门氏菌细胞后，已测定了hisC3076移码标记的回复突变情况。通过改变限定培养基中存在的碳源，结果表明，在葡萄糖存在的情况下，诱变作用降低至接近自发水平，而在氨基葡萄糖、甘露糖、甘露醇、果糖或6 - 磷酸葡萄糖存在时也观察到显著降低。当存在乳酸或甘油时，观察到中等水平的突变体产量，而另一组碳源（葡萄糖酸盐、阿拉伯糖、核糖、琥珀酸盐或酪蛋白水解物）中的任何一种都能使相对大量的突变体被回收。有趣的是，当这些“高产”碳源中的任何一种添加葡萄糖时，又会观察到葡萄糖特有的强烈抑制作用。基于这些结果，可以得出结论，碳源对9AA诱导的回复突变的抑制作用并非葡萄糖所独有，尽管当存在多种碳源时，葡萄糖的抑制作用占主导。对这些发现的可能解释包括，作为葡萄糖跨细胞膜转运的直接结果，9AA被细胞主动排除。为了探究这种可能性，细胞预先在维拉帕米中生长，维拉帕米是一种钙通道拮抗剂，已知它会增加鼠伤寒沙门氏菌中各种9 - 苯胺吖啶衍生物的诱变性。我们发现，用维拉帕米处理后，葡萄糖对9AA诱导的诱变作用的抑制并没有在任何显著程度上得到缓解。在进一步的实验中，使用了两种已知能被主动转运到细胞内但在首次磷酸化步骤后不再代谢的葡萄糖类似物（2'-脱氧葡萄糖和甲基 - D - 葡萄糖苷）。这些类似物抑制几种类型分子进入细胞，但由于它们不会显著降低9AA诱变作用，所以似乎不能用9AA跨细胞膜转运受阻来解释葡萄糖对9AA诱变作用的抑制效果。本文提出了一种基于葡萄糖介导的对易错的、产生突变的DNA修复过程的抑制作用的替代解释。
