Yeast nucleosomal particles: structural and transcriptional properties.

Yeast nucleosomal core particles have been characterized by thermal denaturation, circular dichroism, and digestion with DNase I and with trypsin. Practically all nucleosomal DNA melts in one transition centered at 70 degrees C, and the circular dichroism spectrum is displaced to lower wavelengths as compared to that corresponding to chicken nucleosomal cores. The susceptibility of yeast nucleosomal particles to dissociation by salt is significantly higher than that of chicken nucleosomal cores, a substantial dissociation being observed at 0.5 M NaCl. Treatment of yeast nucleosomal particles with the amino group reagent dimethylmaleic anhydride is accompanied by selective release of histones H2A and H2B. The results indicate not large but significant structural differences between yeast and chicken nucleosomal cores. However, the in vitro transcription properties of complete and H2A.H2B-deficient nucleosomal cores are similar in the two kinds of particles: the histone octamer blocks RNA synthesis, this block being eliminated in part by the partial loss of histones H2A and H2B.