Saha Swati, Jana Bimal, Basu Tarakdas
Department of Biochemistry and Biophysics, University of Kalyani, West Bengal, India.
Int J Radiat Biol. 2007 Jul;83(7):463-9. doi: 10.1080/09553000701371389.
The objective of this study was to investigate how Escherichia coli cells responded at the level of DNA repair, when the cells were subjected to UV (ultraviolet) radiation and heat-stress to induce a DNA repair system (SOS) and heat-shock response, respectively.
The experiments were performed to study the Weigle reactivation of the bacteriophage phiX174 in its host E. coli C/1 cells. Two distinct techniques, top layer agar plating and Western blotting, were employed to measure the plaque count of viable phages and to demonstrate the heat-shock response respectively.
Repair of UV-inactivated bacteriophages in UV-irradiated E. coli cells is known as Weigle reactivation. In the case of the single-stranded DNA containing bacteriophage phiX174, Weigle reactivation occurs only through the inducible SOS repair response. Here we report that when UV-irradiated E. coli cells were transferred to higher temperature, the consequent heat-shock enhanced the reactivation of UV-inactivated phiX174 over normal Weigle reactivation; the enhancement being maximum when the cells were shifted from 30 - 47 degrees C and incubated there for 30 min. The extent of increase of reactivation was less, when the cells were first subjected to heat-shock and then irradiated by UV. Besides heat, ethanol (5 - 10% volume/volume [v/v]), an established heat-shock inducer, also caused enhancement of phage reactivation and the maximum enhancement occurred at 8% v/v ethanol.
We suggest that the SOS and heat-shock responses in E. coli act synergistically in the reactivation of UV-damaged bacteriophage phiX174.
本研究的目的是调查当大肠杆菌细胞分别受到紫外线（UV）辐射和热应激以诱导DNA修复系统（SOS）和热休克反应时，其在DNA修复水平上的反应。
进行实验以研究噬菌体phiX174在其宿主大肠杆菌C/1细胞中的韦格勒再活化。采用两种不同的技术，即顶层琼脂平板培养和蛋白质印迹法，分别测量存活噬菌体的噬菌斑计数并证明热休克反应。
紫外线照射的大肠杆菌细胞中紫外线灭活噬菌体的修复被称为韦格勒再活化。对于含有单链DNA的噬菌体phiX174，韦格勒再活化仅通过诱导型SOS修复反应发生。在此我们报告，当紫外线照射的大肠杆菌细胞转移到更高温度时，随之而来的热休克增强了紫外线灭活的phiX174的再活化，超过正常的韦格勒再活化；当细胞从30℃转移到47℃并在那里孵育30分钟时，增强作用最大。当细胞先受到热休克然后再接受紫外线照射时，再活化增加的程度较小。除了热之外，乙醇（体积分数5 - 10% [v/v]），一种既定的热休克诱导剂，也导致噬菌体再活化增强，最大增强作用发生在8% v/v乙醇时。
我们认为大肠杆菌中的SOS和热休克反应在紫外线损伤的噬菌体phiX174的再活化中协同作用。
