Ultraviolet light induced recovery in Escherichia Coli of radiation damaged bacteriophage deoxyribonucleic acid / by John Randall Silber.

Abstract

The ability of ultraviolet light (UV) 0X17^single stranded and replicative form DNA molecules to produce whole phage when transfected into UV irradiated, calcium treated E. coli K12 hosts was investigated. When IT/ irradiated single and replicative form 0X1TU DNA molecules were transfected into UV irradiated wild type hosts, an enhanced survival of the phage producing ability of the DNA was observed over that seen when the transfection was performed with unirradiated wild type hosts. A similar increase in survival was also found for both types of 0X17 ; t DNA molecules when they were transfected into E. coli deficient in excision repair (uvrA-, uvrBor uvrC-) or recombinational repair (recBor recB-recC-). No enhanced survival was found with recAor lex/V-E. coli hosts. The level of the increased phage producing ability for single stranded 0X17D NA was 1.3 to 1.7 times greater than that for the replicative form DNA in all genetic backgrounds which showed enhanced survival. These results suggest the existence of a UV inducible recovery system which participates in the recovery of UV irradiated 0X17^DNA. This recovery system in dependent upon recA and I ox A regulated function.'; but is independent of excision and recombi national repair. The common genetic requirements for the increased survival of both forms of 0X11 h DNA suggest a common mechanism of recovery for both. The greater survival of the single stranded molecule indicates that it is more susceptible to inducible recovery than the replicative form molecule which may be due to the physical differences between the two. The ability of gamma irradiated 0X17'* single stranded and replicative form DNA to produce whole phage when transfected into a UV irradiated, calcium treated E. coli wild type host was also investigated. By adding appropriate radical scavengers to aqueous solutions of the DNA, it was possible to specify which of the water radiolysis radicals was interacting with the DNA. The maximal enhancement of phage producing ability for both types of DNA was observed under conditions which removed the hydroxyl radical allowing the hydrogen radical and the solvated electron to predominate. Scavenging conditions which removed the hydrogen radical and solvated electron as well as the hydroxyl radical resulted in an enhancement of survival only half as large as the maximum. The same was found to be true for scavenging conditions which removed the hydrogen radical and solvated electron only. These results demonstrate the existence of a UV inducible repair system which mediates in the recovery' of 0X17*1 DNA from gamma ray damage. The mechanism of recovery here could possibly be the same as that which affected the UV inducible recovery of UV irradiated 0X17 '4 DNA. From these results, it can also be concluded that the hydrogen radical and the solvated electron produce a type of damage that is more susceptible to inducible recovery than the hydroxyl radical. The hydroxyl radical appears to produce two classes of damage in both the single stranded and replicative ...