Observation and manipulation of different structural variants of individual cation-DNA complexes in the light...

Using different preparation protocols, different structures consisting of individual cation-DNA complexes are obtained. Vigorous mixing provides globular complexes, with different degrees of packing when poly-L-lysine or histone H1 is the cation. When hydrodynamic shearing is minimized by gentle handling, molecular networks or single cable like structures can be obtained. After 4',6-diamidino-2-phenyl indole (DAPI) fluorescence staining as well as with bright-field microscopy, the cables can be directly visualized in the light microscope. Using a pulsed ultraviolet laser coupled into the microscope (a laser microbeam) stretches of complex can be cut out from networks of poly-L-lysine-DNA complexes which may serve as models for highly extended chromosomes.