Circular superhelical DNA complexes with synthetic oligopeptide: unusual compact structures and influence of bent...

The organization of synthetic oligopeptide trivaline (1) complexes with four types of circular superhelical DNA preparations was studied by electron microscopy. The DNA molecules in the preparations investigated had different sizes ranging from 2.9 kb to 21.0 kb. Two plasmids contained bent DNA sequences from minicircles of kinetoplast DNA of Leishmania gymnodactili and Trypanosoma boissoni. The main structures in all preparations observed were circular compact particles which coincide in their appearance and compaction coefficient (3,5-3,7) with triple rings described earlier. But along with triple rings the new types of compact structures were observed having the shape of a ring with attached rod or the shape of two compact rings attached to each other by a region of compact fiber. The latter structures could be observed in significant quantities in case of DNA preparations longer than 10 kb. The conclusions can be made that due to TVP stimulated compaction of circular DNA molecules compact fibers containing both two or three DNA duplexes arranged side by side can be formed. It is shown that presence of bent DNA sequences stimulates the formation of structures containing more than one triple ring. It demonstrates the possibility of the primary DNA structure influence on the compaction process in case of the circular molecules. The new ways of circular DNA folding described can be of importance for understanding of DNA organization in different cell structures.