Analysis of DNA double- and single-strand breaks by two dimensional electrophoresis: action of micrococcal nuclease on chromatin and DNA, and degradation in vivo of lens fiber chromatin

We describe a novel system for two dimensional electrophoresis at neutral and alkaline pH for determining the double-stranded and single-stranded lengths of DNA. With this system we analysed the mode of micrococcal nuclease digestion of DNA in cellular and SV40 viral chromatin and of supercoiled SV40 DNA. The enzyme reaction occurred in two steps : the enzyme first introduced single-strand breaks, then converted these to double-strand breaks by an adjacent cleavage on the opposite strand. Digestion of cellular chromatin DNA occurred by a similar mechanism. Chromatin fragments produced by limited micrococcal nuclease action contained many single-strand breaks, which may be important when this method is used to prepare chromatin fragments for biochemical and biophysical studies. Nucleosome monomer to tetramer produced at later stages of digestion contained few if any single-strand breaks.

Electrophoresis in gels suspended in hydrophobic solvents

Protein components in mixtures may be separated by zone electrophoresis in columns of gel suspended in hydrophobic solvents. The method is useful for the location of specific antibodies in IgG electrophoretic spectra.

[Use of proteins, covalently bound to agar gel, for specific sorption in electrophoresis]

A method is developed for electrophoretic fractionation of serum proteins in agar gel with simultaneous specific sorption of gamma-globulin fraction, migrating during the electrophoresis through specific immunosorbents incorporated into agar gel. The reaction was carried out in a special apparatus designed for the electrophoresis in two perpendicular directions. The sorbent was separated from impurities by passing the current in the first direction. The unspecific sorbent did not alter the electrophoretic mobility of migrating proteins, but the specific sorbents immobilized completely both antibodies and antigens. The antibodies were shown to bind repeatedly to the immunoglobulins, which had been linked to the sorbent. The method facilitated distinctly the estimation of antigens and antibodies in complicated mixtures. By analogy with affinity chromatography a term "affinity electrophoresis" was used for designation of the method described.