The divalent cation-induced DNA condensation studied by atomic force microscopy and spectra analysis

Three types of DNA condensates in the presence of divalent metal ion (Mg, Mn and Cu) and EB simultaneously have been observed by atomic force microscopy (AFM). In the presence of Mg (II) and EB, DNA molecular exhibits three or four maggot-like branch crossing structures at the same point, which were constructed by some bead-like particles in each branch. However, in the presence of Cu (II) or Mn (II)–EB, DNA molecular forms a network or a semicircular structure, respectively. Their average height was 0.95±0.5 nm (Cu (II)–DNA–EB), 17±5 nm (Mg (II)–DNA–EB) and 12±3 nm (Mn (II)–DNA–EB), respectively. However, DNA molecular or DNA–EB complex still remained a line double-stranded structure. The fluorescence, melting point and CD spectra indicate that the different morphologies induced by divalent metal ion (Mg (II), and Mn (II) and Cu (II)) are related to its binding position in molecular DNA.