HEAT-SHOCK-INCREASED SURVIVAL TO FAR-UV RADIATION IN ESCHERICHIA-COLI IS WAVELENGTH-DEPENDENT

Heat-shock-induced resistance to far-UV (FUV) radiation was studied in Escherichia coli. The induction of FUV resistance was shown to be dependent on the products of the genes uvrA and polA in bacteria irradiated at 254 nm. Heat shock increased the resistance to 280 nm radiation in a uvrA6 recA13 mutant. Heat shock lowered the mutation frequency (reversion to tryptophan proficiency) in wild-type or uvrA strains irradiated at 254 nm. When these strains were irradiated at 280 nm, heat shock did not interfere with the mutation frequency in the wild-type strain, but greatly enhanced mutations in the uvrA mutant. After heat-shock treatment, the wild-type strain irradiated at 254 nm showed increased DNA degradation, indicating enhanced repair activity. However, heat shock did not stimulate SOS repair triggered by FUV. An increased survival of bacteriophages irradiated with FUV and inoculated into heat-shock-treated bacteria was not detected. The possibility that heat shock enhances excision repair activity in a wavelength-dependent manner is discussed.