Privalov defines DNA renaturation as the sequence of the following interrelated steps: base pairing and base stacking. Both these processes required proper orientation of corresponding bases that were needed for the formation of hydrogen bonding. C Tongu, T Kenmotsu, Y Yoshikawa 67 studied shrinking of T4 DNA (166 kbp) samples by adding divalent and trivalent cations. DNA samples were again placed on a mica slide surface, incubated, and dried at room temperature. Then, the DNA on the mica slides was analyzed using AFM imaging with scanning probe microscopy at a constant temperature.