Accessible DNA in Chromatin.

A study has been made of the action of DNAase I and of micrococcal nuclease on chromatin, on the complex of chromatin with polylysine and of DNAase I on DNA ˙ protamine; a comparison of different assay methods of DNAase I action on chromatin is included here. Also, the nature of the polylysine-binding zones in chromatin has been investigated. Measurements of acid-solubility and salt-solubility during digestion show that DNAases I and II degrade almost all of the DNA in chromatin (from various tissues), unimpeded by the chromatin proteins which are released concurrently (and which eventually aggregate on to the degraded DNA). With micrococcal nuclease concurrent release of DNA and of protein occurs similarly; however, full degradation by this nuclease is impeded apparently by aggregation of released protein on to acid-insoluble DNA. In the case of chromatin ˙ polylysine and also DNA ˙ protamine, about half of the DNA is degradable. The results indicate that discrepancies between the findings of previous workers are due to differences in assay of degradation, in conditions of digestion, in enzyme used and probably in methods of preparing chromatin resulting in products varying widely in composition. Also, the results support the previous suggestion that virtually all the DNA in chromatin is associated with protein yet is highly accessible [1], unlike DNA complexed with protamine or polylysine. The polylysine-binding zones in chromatin are discrete, double-stranded, protein-associated regions of DNA which are probably heterogenous from one molecule to another. [ABSTRACT FROM AUTHOR]