Isolation of a hybrid between rat ribosomal RNA and DNA

A procedure for the isolation and purification of a specific hybrid between rat 28S and 18S ribosomal RNA's and nucleolar DNA is described. The method employed includes the following steps: 1) isolation of the nucleolar DNA, 2) hybridization of [14C]rRNA with the nucleolar DNA, and 3) isolation and purification of the rRNA-DNA hybrid complex by chromatography on hydroxylapatite and centrifugation in a CsCl density gradient. In the isolated hybrid complex the RNA:DNA ratio is close to 1:1, and the degree of enrichment of the DNA by the rRNA cistrons is about 1500 times. The hybrid obtained has a sedimentation constant on the order of 20S, is resistant to the action of pancreatic RNase and RNase T1 and sheep brain DNase, and is characterized by high thermostability. Acording to the physicochemical tests used, the rRNA-DNA hybrid complex is a double-stranded poly-nucleotide with an ordered secondary structure.