Compaction of DNA Induced by Like-Charge Protein: Opposite Salt-Effect against the Polymer-Salt-Induced Condensation with Neutral Polymer

We observed the collapsing transition of a DNA molecule in a crowding environment a water-soluable negatively charge protein, albumin. We performed fluorescence microscopic observation to monitor the change in the conformation of individual giant DNA molecules. It is found that DNA molecules exhibit compact conformation above critical concentrations of the negatively charged protein. We interpret this transition in terms of depletion interaction segregation of different polymers driven by excluded volume interaction Interestingly, coexisting salt causes retardation on the collapsing transitin being opposite to the well known phenomenon of DNA compaction in a crowding solution of neutral polymer polymer salt-induced-condensation of DNA (psi-condensation). The possible biological significance of the transition of higher order structure on DNA in a concentrated protein solution is discussed in relation to the highly crowed conditions living cells.