Isolation and characterization of DNA from fixed cells and tissues

DNA was isolated from cultured mammalian cells, liver tissue and Escherichia coli after treatment with the common laboratory fixatives for various periods of time. The cultured cells included the mouse cell strain LM and the Chinese hamster cell strain Don C. Liver tissue was obtained from young adult Chinese hamsters. Ultraviolet spectral absorbance ratios, CsCl buoyant density determinations, melting curves and hyperchromicity were used to characterize the DNA samples. Recovery of “normal” DNA was excellent with most fixatives, but not when formalin was used. Formalin fixation interfered with the isolation procedure, and when DNA was extracted the buoyant densities in CsCl were significantly different from the DNA extracted from unfixed materials, but the T m values were not different.