Effect of sulphur crosslinking on the stability and transition of triple helical DNA.

In continuation to our work on order-order and order-disorder transition in triple stranded DNA when it is bounded to netropsin, we report in this communication the stabilizing/destabilizing effect of disulphide linkage on the phase dynamics of the triplex using the amended Zimm-Bragg theory. It is observed that in contrast to the sequential triplex-->duplex -->single strand melting of the uncrosslinked triplex, crosslinking causes the triplex state to melt directly to the single stranded state, with no apparent intermediary of a duplex state. Since there is no overall difference in the enthalpy of crosslinked and uncrosslinked triplexes, the transition is entropy driven.