[Mechanism of formation of associated oligonucleosomes during electrophoresis]

Here we used DNP electrophoresis to study the mechanism of formation of associated oligonucleosomes (A-particles) which have been previously shown by Weintraub to contain the DNA of silent but not of transcriptionally-active genes from chicken erythrocyte nuclei. We found out that A-particles are generated in the course of electrophoresis and that their assembly is inhibited as the result of redistribution of the most mobile fraction of histones H1 and H5. The mechanism and the conditions for the assembly of A-particles at the start line of DNP electrophoresis are discussed in the paper. The DNA molecules constituting A-particles appeared to be about 60 base pairs longer than the DNA of free oligonucleosomes. Thus in course of nuclease treatment of erythrocyte nuclei two chromatin fractions can be observed, one of them containing the DNA of transcriptionally active genes loses its terminal DNA regions owing to rapid degradation of cleaved nucleosome linkers, while the other containing the DNA of repressed genes maintains its terminal linker DNA and gives rise to the associated oligonucleosomes.