Experimental evidence for asymmetrical shielding of nucleosomal DNA by histones

Abstract

Electron spin resonance study of Mn (II) binding to chromatin and derivatives, including core particles, shows that Mn (II) is a good probe for testing the overall electrostatic balance of the nucleoproteic complex as well as DNA accessibility. Experimental results are in good agreement with a recent model proposed (Mirzabekov A. D. and Rich A. (1979) Proc. Natl. Acad. Sci. USA 76, 1118-1121), for the core particle, in which an asymmetrical shielding of DNA by the protein core is assumed. Furthermore, it was found that the histone H1 hinders a number of charges on the linker DNA in a proportion equal to the net positive charge of the histone itself. This result is interpreted as due to a tighter interaction between the linker DNA and the core histones in the presence of histone H1.