The sedimentation behaviour of ribonuclease-active and -inactive ribosomes from bacteria

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Abstract
The "30 s" and "50 s" ribosomes from ribonuclease-active (Escherichia coli B) and inactive (Pseudomonas fluorescens and E. coli MRE600) bacteria have been studied in the ultracentrifuge. "Charge anomalies were largely overcome by using sodium chloride-magnesium chloride solution, 0.16, made 0-50m[image] with respect to Mg2+. Differentiation of enzymic and physical breakdown at Mg2+ concentrations less than 5m[image] was made by comparing the properties of E. coli B and P. fluorescens ribosomes. Ribonuclease-active ribosomes alone showed a transformation of "50 s" into 40-43 s components. This was combined with the release of a small amount of "5 s" material which may be covalently bound soluble ribo-nucleic-acid (RNA). Other transformations of the "50s" into 34-37 s components were observed in both ribonuclease-active and -inactive ribosomes at 1.0-2.5m[image]-Mg2+ and also with E. coli MRE600 when EDTA (0.2m[image]) was added to a solution in 0.16[image]-sodium chloride. Degradation of ribonuclease-active E. coli B ribosomes at Mg2+ concentration 0.25m[image] or less was coincident with the formation of 16 s and 21 s ribonucleoprotein in P. fluorescens, and this suggested that complete dissociation of RNA from protein was not an essential prelude to breakdown of the RNA by the enzyme. As high Cs+/Mg2+ ratios cause ribosomal degradation great care is necessary in the interpretation of equilibrium-density-gradient experiments in which high concentrations of caesium chloride or similar salts are used. The importance of the RNA moiety in understanding the response of ribosomes to their ionic environment is discussed.