Biochemistry of DNA lesions.

Ionizing radiation produces a range of damage types in cellular DNA. All damage types do not have the same biological significance. Here arguments are presented supporting the view that lesions in which damage is present on both strands in a local region of the DNA (locally multiply damaged sites--LMDS) will present problems for cellular repair processes. We have previously shown that lesions produced in DNA by individual OH radicals, i.e., single OH species acting alone, are ineffective in mammalian cell killing [J.F. Ward, W.F. Blakely, and E.I. Joner, Radiat. Res. 103, 383-392 (1985)]. We have similar evidence in mutagenesis studies (Ward and Calabro-Jones, unpublished data). Thus the formation of such damage by individual OH radicals formed by ionizing radiation would be similarly ineffectual. Earlier [J.F. Ward, Radiat. Res. 86, 185-195 (1981)] we suggested that OH-radical scavenging studies were consistent with the scavenging of OH radicals in volumes of high radical density, spurs, etc., i.e., in volumes which, when they overlap the DNA, will cause the production of LMDS. The individual constituent lesions of LMDS will be formed as a result of direct ionization or as a result of an OH-radical attack. Both mechanisms can lead to base damage or strand breakage. It is clear that damage in both bases of a deoxyribonucleotide pair leads to loss of base sequence information and can be repaired correctly only by accident or in a recombinational process.(ABSTRACT TRUNCATED AT 250 WORDS)