MONOMERIC, DIMERIC AND TRIMERIC BINDING OF A BIS-NETROPSIN TO DNA

An unusual 3:1 stoichiometry for complex formation between an elongate d bis-netropsin compound and its binding site on DNA has been observed . Circular dichroism measurements distinguish two types of complexes f ormed between this bis-netropsin and poly[d(A-T)]. poly[d(A-T)]. The f irst type is characterized by a 1:1 saturating ratio of bound molecule s per ten base pairs. Formation of the second type results from the co operative binding of two additional bis-netropsin molecules to the fir st type of complex. In contrast to these results observed for binding to the alternating polynucleotide, only the 1:1 type of complex is for med when this ligand binds to the homopolymer poly(dA). poly(dT).