Nuclease digestion in between and within nucleosomes.

In the course of digestions of rat liver nuclei with micrococcal nuclease the size of the nucleosomal DNA is shortened by 50-60 nucleotide pairs from starting lengths of about 200, 400, 600, 800, etc. nucleotide pairs in the monomeric and oligomeric nucleosomes, respectively. Acid soluble DNA material is created relatively slowly as compared to the rate of formation of subnucleosomal material. More DNA with lengths in between the 200, 400, etc. nucleotide pairs of nucleosomal DNA is formed when digestions with micrococcal nuclease are carried out at 0 to 10 degrees C compared to 40 degrees C. With DNAase II, on the other hand, formation of a 200 nucleotide pair pattern is favoured at the low temperatures. Apparently, the accessibility of potential cleavage sites in between and within nucleosomes depends strongly on the conditions of digestion. Possible reasons for this dependence are discussed.