Repair of near (365 nm)- and far (254 nm)- UV damage to bacteriophage of Escherichia coli

Intact bacteriophages were irradiated at 365 nm or 254 nm and then analyzed for DNA photoproducts or injected into their bacterial host to test susceptibility of the damage to both phage and host-cell mediated repair systems. Both thymine dimers and single-strand breaks were induced in the phage DNA by 365 nm radiation. The dimers appeared to be the major lethal lesion in both repair deficient bacteriophage T4 and bacteriophage lambda after 254 nm or 365 nm irradiation. Damage induced in T4 by either wavelength was equally susceptible to x-gene reactivation. v-gene reactivation acted on a larger fraction of the near-UV damage. The host-cell mediated photo-reactivation system was only slightly less effective for near-UV damage but host-cell reactivation (survival of phage lambda on uvr+ and uvr- host) was effective against a far smaller section of near-UV damage than far-UV damage. Weigle-reactivation (far-UV induced) of near-UV damage to phage lambda was not observed. The results suggested that unless the near-UV damaged phage DNA is repaired immediately after injection, the lesions rapidly lose their susceptibility to repair with a consequent loss of activity of the phage particles. (author)