Filippov V D, Zagoruiko E E
Genetika. 1976;12(11):115-20.
To test a suggestion that mutation frequency decline (MFD) in UV-irradiated bacteria starved by nitrogen sources is caused by long delay of the first postradiation cycle of DNA replication, we used a strain 1201-05 of Bacillus subtilis 168 (ade6 met5tsdnaC) which does not synthesize DNA at 42 degrees C. In a suspension of UV-irradiated cells of this strain which is incubated at 42 degrees in liquid deprived by nitrogen sources, a decrease of frequencies of Ade+ and Met+ revertants is observed. This shows that the mechanism responsible for MFD normally operates at higher temperature. Such a level of decline is not observed in a suspension incubated in nutritional medium when the DNA replication is blocked by non-permissive temperature for the same period as in starved cells. On the basis of these facts it is concluded that MFD in suspension of bacteria starved by nitrogen sources can not be caused only by delay of postradiation replication of DNA.
为了验证关于氮源饥饿的紫外线照射细菌中突变频率下降（MFD）是由DNA复制的首次辐射后周期长期延迟所导致的这一假说，我们使用了枯草芽孢杆菌168（ade6 met5 tsdnaC）的1201 - 05菌株，该菌株在42℃时不合成DNA。在该菌株经紫外线照射的细胞悬浮液中，于42℃在无氮源液体中孵育时，观察到Ade +和Met +回复突变体频率降低。这表明负责MFD的机制通常在较高温度下起作用。当DNA复制在与饥饿细胞相同的时间段内被非允许温度阻断时，在营养培养基中孵育的悬浮液中未观察到这种下降水平。基于这些事实，可以得出结论，氮源饥饿细菌悬浮液中的MFD不能仅由辐射后DNA复制的延迟引起。
