Repulsive/attractive interaction among compact DNA molecules as judged through laser trapping: difference between linear- and branched-chain polyamines

It is well known that polyamines induce a folding transition from an elongated coil to a compact globule state for giant DNA larger than several tens of kbp (kilo base pairs). Here, we studied the interaction between compact DNA molecules in the presence of linear and branched-chain isomers of polyamines. We compared the stability of the assembly among plural number of compact DNA molecules generated by laser trapping. As a result, the assembly of compact DNAs with a linear-chain polyamine is stable even after the laser is switched off. On the other hand, the assembly of DNAs with a branched-chain polyamine disperses into individual compact DNAs when the laser is switched off. Thus, compact DNAs with linear- and branched-chain polyamines attract and repel each other, respectively. This difference in the effects of linear and branched polyamines is discussed in terms of the steric interaction between negatively charged double-strand DNA and cationic polyamines. Graphical abstract