Nucleic Acids Research, Vol 25, Issue 8 1502-1510, Copyright © 1997 by Oxford University Press
S Jennewein and MJ Waring
In order to clarify the role of the purine 2-amino group in the recognition
of DNA by small molecules we have examined the binding of actinomycin D and
echinomycin to artificial DNA molecules asymmetrically substituted with
inosine and/or 2,6-diaminopurine (DAP) in one of the complementary strands.
These DNAs, prepared by a method based upon PCR, present various potential
sites for antibiotic binding, including several containing only a single
purine 2-amino group in different configurations. The results show
unambiguously that the presence of two 2-amino groups is mandatory for
binding of actinomycin D to double-stranded DNA. In the case of echinomycin
only one purine 2- amino group is required for remarkably strong binding to
the asymmetric TpDAP.TpA dinucleotide step, but the CpDAP.TpI step (which
also contains only a single purine-2 amino group) does not afford a binding
site. Evidently, removing a 2-amino group (G-->I substitution) is
dominant over adding one (A-->DAP substitution). No sequences containing
just a single guanine residue are acceptable. The possibility is raised
that replacing guanosine with inosine may do more than remove a group
endowed with hydrogen bonding capability and interfere with ligand binding
in other ways. The new methodology developed to construct asymmetrically
substituted DNA substrates for this work provides a novel strategy that
should be generally applicable for studying ligand-DNA interactions, beyond
the specific interest in drug binding to DNA, and may help to elucidate how
proteins and oligonucleotides recognize their target sites.
ARTICLES
Footprinting of echinomycin and actinomycin D on DNA molecules asymmetrically substituted with inosine and/or 2,6-diaminopurine
Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QJ, UK.
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