Sequence specificity of DNA cleavage by bis(1,10-phenanthroline)copper(I): effects of single base pair transitions on the cleavage of preferred pyrimidine-purine-pyrimidine triplets

The cleavage of DNA restriction fragments by bis(1,10-phenanthroline)copper(I) [[(OP)2CuI]+] is sequence dependent: the trimer TAT is most strongly preferred, while the trimer TGT and tetramers TAAT, TAGT, and CAGT are strongly to moderately preferred [Veal, J. M., & R. L. (1988) Biochemistry 27, 1822-1827]. [(OP)2CuI]+ cleavage of a series of oligonucleotide duplexes of the type 5'-CCCTPyPuPyCCCC-3'/3'-GGGAPuPyPuGGGG-5' (Py = pyrimidine; Pu = purine) was examined to determine the effects of purine substituents in the central triplet on specificity. The relative cleavage rates of different PyPuPy triplets in oligomers were similar to those observed for restriction fragments. The undecamer duplex containing the trimer TAT (TTATC) was most preferentially cleaved, predominantly at the central adenosine and the adjacent 3'-thymidine. Duplexes differing from TTATC by a single A.T----G.C transition in the central triplet were cleaved at significantly reduced rates relative to TTATC, the order of preference being TAT greater than TGT greater than TAC greater than CAT. By contrast, duplexes differing from TTATC by a single A.T----I.C transition were cleaved at rates similar to those for TTATC when the transition occurred at the 5'-pyrimidine or central purine [i.e., C(.I)AT and TIT]. A duplex containing the trimer TAC(.I) was cleaved at a reduced rate similar to the duplex containing TAC(.G). The guanine 2-amino group at positions 1 and 2, but not position 3, of a 5'-PyPuPy-3' trimer is therefore implicated as a strong inhibitor of DNA binding by the copper-phenanthroline complex.(ABSTRACT TRUNCATED AT 250 WORDS)