UNUSUAL BEHAVIOR EXHIBITED BY MULTISTRANDED GUANINE-RICH DNA COMPLEXES

The structural properties of oligonucleotides containing two different types of G-rich sequences at the 3'-ends were compared. It is shown t hat oligonucleotides with uninterrupted runs of guanine residues at th e 3'-end, e.g., d(T(15)G(12)), from multistranded structures stabilize d by guanine-guanine interactions. The chemical and physical propertie s of these complexes differ from those of the complexes formed by olig onucleotides with telomere-like sequences, e.g., d(T(15)G(4)T(2)G(4)). In methylation protection and methylation interference experiments, w e found all the guanines in complexes formed by d(T(15)G(15)) and d(T( 15)G(12)) to be accessible to methylation. Furthermore, the methylated monomers retain the ability to polymerize. This contrasts with the in accessibility of the guanines in d(T(15)G(4)T(2)G(4)) to methylation a nd the inability of the methylated monomer to form supramolecular stru ctures. The stoichiometry of the complexes arising from the two types of oligonucleotides also differs. The complexes formed by d(T(15)G(15) ) consist of consecutive integer numbers of DNA stands, whereas comple xes formed by telomere-like oligonucleotides contain 1, 2, 4, or multi ples of four strands. Magnesium ions favor formation of high molecular weight complexes by d(T(15)G(15)) and d(T!(15)G(12)), but not by d(T( 15)G(4)T(2)G(4)). The d(T(15)G(15)) and d(T(15)G(12)) complexes have v ery high thermal stability compared with telomeric complexes. However, at low temperatures, the thymine bases within the telomeric motif, TT GGGGTTGGGG, appear to allow for the formation of stable high-molecular weight species with a longer nonguanine portion. (C) 1998 John Wiley & Sons, Inc.