The modified base and sugar moieties, 8-oxo-7,8-dihydroadenine (HO8A),8-methoxyadenine (MeO8A),8-methoxyguanine (MeO8G) and 9-[(2-hydroxy-1-(hydroxymethyl)-ethoxy)-methyl]-adenine (acA), were chemically introduced in place of the adenine or guanine in the octa-deoxyribonucleotides [d(GGAATTCC)] containing recognition sequence of Eco RI. to the regular DNA-fragment.