Reactivation of phage from lethal ultraviolet damage in DNA

Abstract

Reactivation phenomena can be used to discriminate between different types of lethal effects in phage. This report deals with the relationship between photorestoration (PhR) and u gene reactivation (uR). The uR is initiated by the u gene in T4 phage in which it exists obligatorily, but not in T2. The lethal uv lesions reactivable by PhR infringe to a great extent on those reactivable by uR; this easily explains the control of PhR by the u gene. A u/ sup +/ mutant of T4, which behaves as T2 with respect to the UV sensitivity and photoreactivation, was isolated. Under conditions of multiple infection, in which the majority of the uv lesions are repaired by multiplicity reactivation (MR), the u and u/sup +/ phage have the same residual sensitivities. According to the Barricelli theory these sensitivities are attributable to the uv hits on vulnerable centers.'' These are not u reactivable, but 50% are photorestorable. It is presumed that these are the photorestorable lesions observed in T4 in simple infection. Among the uv lesions which inactivate the phenotypic expression of the rII-B cistron, 25% are reactivable by PhR or uR. The possible relationships between the different reactivation phenomena and their possible connectionsmore » with photochemical changes as well as their effect on lesions or replication and functional processes are discussed. (tr-auth)« less