Studies on the substrate specificity of the T4 excision repair endonuclease

Abstract

Previous studies have shown that the v gene of bacteriophage T4 codes for an endonuclease that specifically attacks pyrimidine dimer sites in UV-irradiated DNA. The present studies have examined the role of this endonuclease in the repair of DNA damaged by nitrogen mustard, N-methyl- N′-nitro- N-nitrosoguanidine (NTG), mitomycin C and 4-nitroquinoline- N-oxide. The observation by Harm that the v gene product of phage T4 facilitates repair of UV damage to the host DNA of excision-repair defective strains enabled us to test whether it does the same with other cellular DNA lesions. It was shown that infection of UV-irradiated E. coli B s−1 with UV-inactivated phage T4 v+ resulted in rescue of a certain fraction of the host cells. However no v gene mediated repair E. coli B s−1 was observed following treatment with the chemical agents mentioned. Furthermore, though phage T4 v 1 is more sensitive to UV-irradiation than phage T4, there was no observed difference in the sensitivity of these phages to nitrogen mustard or NTG. On the basis of these observations it was concluded that the v gene coded endonuclease of T4 is specific for the excision repair of pyrimidine dimers and does not participate in the repair of chemically damaged DNA. In vitro enzymatic degradation of DNA alkylated with nitrogen mustard was observed, but it is probable that this degradation is not part of a repair reaction in vivo.