title: Binding of actinomycin D to the T(G)nT motif of double-stranded DNA: determination of the guanine requirement in nonclassical, non-GpC binding sites.
abstract: Strong binding of the antitumor antibiotic actinomycin D to the sequence 5'-TGGGT-3' in double-stranded DNA was recently established by equilibrium binding studies (Bailey et al., 1993). Actinomycin D binding to this -TGGGT- containing sequence was shown to be comparable to that of an -XGCY- containing oligonucleotide (Ka approximately 10(6) M-1). Investigation of -TGGGT- as a high-affinity binding site for actinomycin D follows from our 1989 sequencing study (Rill et al., 1989) in which the photoaffinity analog of actinomycin D (7-azidoactinomycin D) was used to determine DNA base sequence specificities and neighboring base effects. The studies presented here examine the guanine requirements for actinomycin D binding to such nonclassical (non-dGpC) sites by varying the number of central guanine residues in a series of selected duplex oligonucleotides. The central -T(G)nT- motif varies from n equals 1 to 4. Actinomycin D binding to each of these undecamers is characterized and correlated with binding to oligonucleotides of identical length and similar sequences that contain classical dGpC binding sites. Binding affinities of actinomycin D to this series of oligonucleotide duplexes (10 degrees C) can be summarized as -TGGGT- > -TGGT- > TGGGGT- > -TGT. The kinetics of SDS-induced dissociation of actinomycin D from these oligonucleotides reveal single-exponential decays with duration dependent on the sequence at the binding site. With the exception of the -TGGGT- containing oligomer, dissociation times for the T(G)nT duplexes were drastically different and much shorter than times obtained for the dissociation of actinomycin D from oligonucleotides having classical dGpC sites.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Chemistry, University of Mississippi, University 38677.
authors.forename: S A
authors.initials: SA
authors.lastname: Bailey
authors.forename: D E
authors.initials: DE
authors.lastname: Graves
authors.forename: R
authors.initials: R
authors.lastname: Rill
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D003609:Dactinomycin / Q000737:chemistry / Q000378:metabolism*; D006147:Guanine / Q000737:chemistry / Q000378:metabolism; D006358:Hot Temperature; D007364:Intercalating Agents / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D009691:Nucleic Acid Denaturation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D007364:Intercalating Agents; D009838:Oligodeoxyribonucleotides; D003609:Dactinomycin; D006147:Guanine; D004247:DNA