Abstract
Covalently closed circular DNA undergoes temperature-dependent change in helical twist. Nucleosome core particles [from chicken erythrocytes] were reconstituted onto closed circular DNA and the thermal untwisting of the DNA was measured as a function of nucleosome density. The DNA associated with the nucleosome core particle does not alter its twist when the temperature is varied between 4.degree. C and 37.degree. C, and the length of DNA prevented from thermal untwisting includes the linker as well as the core DNA.