Dnase Ⅰ-Resistant and Species in HeLa Cell and Atomic Force Microscopic Observation

A DNA sample extracted from HeLa cells was digested by DnaseⅠ and found to contain two enzyme-resistant species (termed as B and C).Results from gel electrophoresis showed that the fragment sizes of species B were more than 20000 bp and that of species C were between 40-50 bp.All these two species were different from the standard duplex DNA in the image of atomic force microscopy,among which species B exhibited characteristics similar to a reported unusual form of λ-DNA.Species C has not been reported and was assumed to be quadruplex according to its apparent width and height.In addition,the fluorescence experiments showed that they can also interact with EB and increase its fluorescence intensity.