Torus-shaped particles formed due to intermolecular condensation of circular DNA upon interaction with synthetic tripeptide.

The morphology of complexes between relaxed circular plasmid pBR322 DNA and tripeptide L-Val-L-Val-L-Val-NH-NH-Dns (TVP) at different peptide/DNA ratios was studied by electron microscopy. The results show that interaction of TVP with circular DNA leads to the formation of perfect torus-shaped particles. The torus parameter measurements offer the possibility to conclude that DNA condensation observed is of intermolecular nature. On the basis of the analysis of the structures corresponding to the early stages of DNA compaction the model for intermolecular condensation of circular DNA into torus-shaped particles is proposed.