CHARACTERIZATION OF THE ELECTROPHORETIC PROPERTIES OF NUCLEOSOME COREPARTICLES BY TRANSVERSE POLYACRYLAMIDE PORE GRADIENT GEL-ELECTROPHORESIS

Transverse pore gradient gel electrophoresis, previously applied to be nt DNA, has extended the usefulness of the gel retardation assay in tw o ways: (i) by differentiating between different DNA conformations; (i i) by providing information regarding the physical properties of DNA. In the present study, similarly extended information is obtained with regard to a well-characterized DNA-protein complex, the chicken erythr ocyte nucleosome core particle. (i) The winding of DNA around the prot ein core constrains the DNA which renders its Ferguson curve (migratio n distance vs. gel concentration) similar to that of kinetoplast DNA, i.e. it intersects sharply with the Ferguson curves of linear DNA stan dards. By contrast, the deproteinized nucleosome DNA exhibits a Fergus on curve similar to linear standards of the same lenght. (ii) Interpre tation of the Ferguson curve based on a mathematical model shows that the nucleosome exhibits a linear Ferguson plot [log(mobility) vs. gel concentration]. This is similar to and characteristic of spherical pro teins, contrasting with the concave plot typical for linear and bent D NA. (iii) The effective size of the nucleosome, evaluated in terms of an ''equivalent sphere'' (i.e. a hypothetical spherical particle with a radius, R(es), having the same electrophoretic mobility as DNA for a particular set of experimental conditions), remains invariant across the gel concentration range of 3-9%T. This is similar to proteins and bacteriophages and contrasts with the progressive decline of R(es) wit h increasing gel concentration observed for linear DNA and the deprote inized nucleosomal DNA.