Isolation and purification of transcriptionally active ribosomal chromatin from the slime mould, Physarum polycephalum.

In the acellular slime mold Physarum polycephalum the ribosomal genes are all located on linear, extrachromosomal DNA molecules which are clustered in the nucleolus. This report describes the isolation and purification of these ribosomal genes as functionally active chromatin particles. Nucleolar lysates are fractionated by gel filtration to remove ribosomal precursors and other soluble material. The ribosomal chromatin is subsequently separated from contaminating nuclear chromatin by a sucrose gradient centrifugation step. This procedure allows the isolation of the ribosomal genes as intact nucleoprotein particles, which are now amenable to a biochemical analysis of their structural and functional properties.