COMPLEX OF OSMIUM-TETROXIDE WITH 1,10-PHENANTHROLINE BINDS COVALENTLYTO DOUBLE-STRANDED DNA

Complex of osmium tetroxide with 1,10-phenanthroline (Os,phen) reacts with double-stranded B-DNA in contrast to osmium tetroxide, pyridine a nd other osmium structural probes which show a strong preference for s ingle-stranded DNA (ssDNA) (Palecek, E. in Abelson, J.N., and Simon, M .I. (eds), Lilley, D.M.J., and Dahlberg, J.E., (volume eds.), Methods in Enzymology, Vol. 212, DNA Structures, part B., Academic Press, 139- 155 (1992)). Modification of negatively supercoiled DNA (scDNA) with O s,phen changes the DNA electrophoretic mobility inducing the DNA relax ation at lower degrees of modification followed by formation of positi ve supercoils at higher modification extents. Electrophoretic mobility of the Os,phen-modified DNA fragments in agarose gel is almost unchan ged while a strong retardation of the same fragments is observed in po lyacrylamide gels. Os,phen-modified DNA is hypersensitive to nuclease S1. Cleavage of this DNA by restriction enzymes is selectively inhibit ed showing a preference of Os,phen for TA and AT dinucleotide steps. D NA modification by Os,phen is inhibited by low and moderate concentrat ions of MgCl2. The covalent binding of Os,phen to double-stranded DNA (dsDNA) is preceded by noncovalent interactions (probably intercalatio n) inducing DNA structural changes; the shape of the Os,phen-modified DNA molecule appears to be severely deformed.