Palindromic oligonucleotides containing 7-deaza-2'-deoxyguanosine: solid-phase synthesis of d[(p)GG*AATTCC] octamers and recognition by the endodeoxyribonuclease EcoRI.

Octadeoxynucleotides with the sequence d[(p)GG*AATTCC] have been prepared by solid-phase synthesis employing regular and base-modified phosphoramidites. These oligomers which contain an isosterically altered recognition sequence of the endodeoxyribonuclease Eco RI form duplexes under appropriate salt conditions. Since G* can represent 7-deaza-2'-deoxyguanosine the oligomers were used as probes to study their cleavage by the endodeoxyribonuclease Eco RI. The enzymatic hydrolysis of the modified octamer was strongly decreased compared to the regular DNA-fragment. This shows that guanine N-7 located at the cleavage site is important for the recognition process by the enzyme. The residual enzymatic activity is discussed on the basis of reduced specificity towards the recognition fragment. The fact that this cleavage occurs already under regular conditions indicates that the process described here bases on an intrinsic property of the oligomer and is different from the star activity.