Cloning And Expression Of Glutathione Gene And Its Uv-Resistance Function

Glutathione (GSH) is a kind of low-molecular-weight thiol made up by L-glutamic acid, L-cysteine and glycin. The effect of GSH on the ultraviolet (UV) induction of lambda prophage was investigated in lysogenic Escherichia coli in present study. The data showed that extracellular GSH could inhibit the UV induction of lambda prophage. The inhibitory rates were concentration dependent, and the maximal rate obtained was over 93 % with 3.0 mol/L GSH. The effect was also measured in different lambda lysogens: a wild-type strain (wt), an isogenic glutathione-deficient strain isolated by disrupting the gamma-glutamylcysteine synthetase (gshI) gene, and three isogenic strains producing increased amounts of GSH due to the overexpression of gshI and/or gshII gene. The result showed that when subjected to UV irradiation (254 nm, 60 J/m~2), GSH-deficient strain was approximately five fold more sensitive to be lysed than the wild-type strain, whereas the strain with highest intracellular GSH levels was only 28 % susceptible to be lysed. Correspondingly, the UV-resistance of different lambda lysogens is correlated to their intracellular GSH levels. The survival rate of the strain with highest intracellular GSH levels was more than eight fold when compared to the wild-type strain, while the survival rate of the GSH-deficient strain was determined to be only 16 %. With electron spin resonance (ESR) and spin trapping techniques, we observed that free radical signals occurred in the suspensions of UV irradiated lysogenic cells and the intensity of signals was influenced by GSH levels. These results indicate that GSH can significantly inhibit the UV induction of lambda prophage, and that this effect is correlated to its capacity to scavenge free radicals generated in the process of UV irradiation.