BINDING OF MAGNESIUM-IONS AND ETHIDIUM-BROMIDE - COMPARISON OF RIBOSOMES AND FREE RIBOSOMAL-RNA

Comparative studies of free ribosomal RNA and ribosomes were made with two probes, Mg++ ions and ethidium bromide, which interact with RNA in different ways. E.coli 16 S rRNA and 30 S ribosomes were equilibrated with four different buffers. Equilibration required several days at 4° and several hours at 37° In all buffers ribosomes bound more Mg than free rRNA, the difference sometimes reaching 20-30%. Ribosomes were more resistant than free rRNA to heat denaturation and their denaturation was more highly cooperative. Ribosomes that bound more Mg++ had higher denaturation temperatures. Ethidium bromide. Fluorescence enhancement studies of ethidium intercalation showed the free 16 S rRNA to have 50-80 binding sites per molecule. A large fraction of these sites were present and accessible in the ribosome, but their ethidium-binding constants were reduced by an order of magnitude. In addition, free rRNA contained a small number of very strong binding sites that were virtually absent in the ribosomes. © 1979 Information Retrieval Limited.