Structural organization of kinetoplast DNA and its compaction in the in vitro model system.

Electron microscopic studies of Leishmania gymnodactyli cells lysed at hypotonic conditions showed that the structures identified as kinetoplast DNA have the appearance of loose accumulations of crossed and sometimes branched rod-like structures 100 to 200 nm long and 20 nm thick. The compaction of isolated kinetoplast DNA (kpDNA) caused by interaction with synthetic tripeptide--dansylhydrazide trivaline--was also studied. The analysis of the structures arising at different steps of compaction showed that the minicircles are compacted forming rod-like structures where minicircle double-stranded DNA segments are closely associated side by side in a manner which was earlier described for initial compaction stages of "triple rings". These rod-like structures resemble in their appearance the structures found in lysed cell preparations obtained according to Miller's method. Branching of rod-like structures can be the consequence of minicircle catenation. In vitro compaction is completed with the formation of a compacted network, its diameter being 3 to 6 times smaller as compared with the initial one.