Quantitative analysis of the digestion of yeast chromatin by staphylococcal nuclease

The DNA in intranuclear yeast chromatin is protected from rapid staphylococcal nuclease degradation so as to yield an oligomeric series of DNA sizes. The course of production and disappearance of the various oligomers agrees quantitatively with a theory of random cleavage by the enzyme at uniformly susceptible sites. The sizes of the oligomers are integral repeats of a basic size, about 160 base pairs, and 80-90% of the yeast genome is involved in this repeating structure. Within this repeat there exists a 140 base pair core of more nuclease-resistant DNA. During the course of digestion, the sizes of the oligomers decrease continuously. The widths of the distribution of DNA sizes increase in order: monomer (1 X repeat size, half width = 5-7 base pairs) less than dimer (2 X repeat size, half width = 30 base pairs) less than trimer (3 X repeat size, half width = 40-45 base pairs). The yeast genome thus seems to have variable spacing of the nucleaseresistant cores, to produce the average repeat size of about 160 base pairs. Also, the presence of more than one species of monomer and dimer at certain times of digestion suggests a possible heterogeneity in the subunit structure.