Observation of two forms of conformations in the reentrant condensation of DNA.

Reentrant condensation of DNA in the presence of spermidine (SPD) is studied by gel electrophoresis (GEP). It is found that the reentrant condensation of DNA induced by SPD can produce a reentrant jamming of DNA molecules at the liquid-gel interface during GEP. However, not all the DNA are jammed at the interface indicating that there are different forms of condensed DNA. A model of condensed DNA consisting of two conformations can be used to explain the experimental observations. A phase diagram of the reentrant condensation based on the jamming states of DNA in terms of the length of DNA (L) and concentration of SPD is constructed. Furthermore, no charge inversion is observed during the reentrant transition.