Staphylococcal nuclease and pancreatic DNase cleave the DNA within the chromatin core particle at different sites.

Staphylococcal nuclease (micrococcal nuclease) and pancreatic DNase (DNase I) were used to digest HeLa chromatin core particles which had been labeled with 32P at their 5'-DNA termini. In contrast to DNase I, which cleaves core particle DNA at 10-nucleotide intervals from the 5' termini, staphylococcal nuclease cleaves core particle DNA at different sites, both fewer in number and less regularly spaced. Thus, it is unlikely that simple physical protection of DNA is the sole mechanism whereby chromosomal proteins restrict the nucleolytic cleavage of chromatin; furthermore, it seems likely that these nucleases may recognize different geometric configurations along the chromatin core particle.