- Abstract— Antibodies directed toward 8-(2-hydroxy-2-propyI)-deoxyguanosine-5′-monophosphate (8-hpdGMP), a product of the photoalkylation of deoxyguanosine-5‘-monophosphate with 2-propanol, were shown to be highly specific and sensitive in detecting 8-hpdGMP residues in photoalkylated DNA. The antibodies were further used to determine the distribution of modified guanine residues in DNA. The irradiated DNA was digested with restriction enzymes and the fragments obtained were separated electrophoretically and blotted onto diazotized paper. The covalently bound DNA fragments were probed with the antibodies and then with 125I Staphylococcus aureus protein A. These experiments indicate a non-random distribution of modified guanine residues in øX174 RF DNA molecules.