ON THE NATURE OF NUCLEOLAR RNA

Abstract

Structural RNA of cytoplasmic ribosomes of pea seedlings can be hybridized with denaturated pea-seedling DNA. Such hybridization, at RNA saturation, involves 0.3% of the total genomal DNA indicating that a multiplicity of DNA stretches are involved in the production of ribosomal RNA. The RNA of the nucleolus also hybridizes with the DNA stretches which are complementary to ribosomal RNA. Nucleolar RNA would appear therefore to contain ribosomal RNA. Only a minority of ribosomal RNA cistrons occur in the nucleolar DNA while the vast majority is to be found in the chromatin. It is concluded that the bulk of the ribosomal RNA[long dash]if not all[long dash]is manufactured by nonnucleolar regions of the chromatin and that the ribosomal RNA is then transferred into the nucleolus for final assembly into ribosomes.