[Arrangement in chromatin of DNA sites accessible to Serratia marcescens endonuclease].

Splitting of DNA in rat thymus nuclei by Serratia marcescens endonuclease has been studied. DNA fragments were analyzed by gel electrophoresis. Obtained data indicate that the internucleosomal DNA interacts with histones octamer and is cut by endonuclease to fragments multiple of 10 nucleotides. Limits digestion of nuclei with Serratia endonuclease (up to 50% of DNA acid solubility) leaves in a nondegraded form the chromatin fragments including DNA pieces up to 1000 bases in size-resistant DNA. Partly, the resistant DNA has properties of single-stranded molecules. These data are interpreted so that Serratia endonuclease is able to hydrolyse with some preference one of the DNA strands in chromatin. It can be considered as an evidence of different modes of interaction of the histone core with the two DNA strands.