CHIRALITY OF DNA SUPERCOILING ASSIGNED BY SCANNING FORCE MICROSCOPY

Reproducible images of pBR322 plasmid molecules have been recorded by scanning force microscopy under 1-propanol. Most of the plasmids were found in a coiled state. The supercoiled molecules of our samples look like branched or unbranched interwound superhelixes. This is consiste nt with available electron microscopy data on circular DNA molecules. By applying a stratigraphic analysis which takes advantage of the heig ht information contained in the scanning force microscopy images, it i s possible to assign the chirality of the local supercoiling of the in dividual molecules.