Patterns of protein synthesis in a growth delay mutant ( nuv) of Escherichia coli after treatment by near-UV radiation or hydrogen peroxide

Abstract

When Escherichia coli cells are stressed by hydrogen peroxide (H 2O 2), synthesis of a large number of proteins is repressed, while several other proteins are induced. Since there is evidence that some lethal effects of near-UV (NUV) radiation may be directly or indirectly due to hydrogen peroxide generated by NUV light, treatment of cells with NUV radiation or H 2O 2 might be expected to repress and induce the same set of proteins. In this study, we compared the effects of H 2O 2 and NUV irradiation on patterns of protein induction and/or repression which were separate from the 4-thiouridine-dependent response using growth delay mutants ( nuv). Concentrating initially on the proteins that ceased synthesis following NUV irradiation in an nuv mutant, we observed that these were not the same as those that ceased synthesis following H 2O 2 treatment. Inspection of two-dimensional polyacrylamide gel electrophoresis proteins indicated that NUV irradiation repressed synthesis of a different set of proteins, although there was some overlap between the two (45%). It was also observed that the new proteins which appeared after each of the two treatments were different. This suggests that the induction and/or repression of new proteins following NUV irradiation is not triggered solely via oxidative stress, although there is some overlap between the proteins that are induced or repressed following the two treatments.