title: Binding of magnesium ions and ethidium bromide: comparison of ribosomes and free ribosomal RNA.
abstract: 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. Mg++. E. coli 16 S rRNA and 30 S ribosomes were equilibrated with four different buffers. Equilibration required several days at 4 degrees and several hours at 37 degrees. 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.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D004926:Escherichia coli / Q000378:metabolism; D004996:Ethidium; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D009690:Nucleic Acid Conformation; D012335:RNA, Ribosomal / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism* / Q000648:ultrastructure; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D012335:RNA, Ribosomal; D004996:Ethidium; D008274:Magnesium