Composition of ribosomes of an extremely halophilic bacterium

Amino acid analyses and electrophoresis on starch—urea gels have shown that the ribosomes of the extremely halophilic bacterium, Halobacterium cutirubrum, contain a majority of acidic proteins with isoelectric points of about 3·9 and a smaller proportion of basic proteins with isoelectric points above about 8·5. From analyses of magnesium and potassium, it is concluded that magnesium ions probably stabilize the RNA moiety as in other ribosomes, and that potassium ions neutralize negative charges, thereby enabling the acidic proteins to be bound to the ribosomal RNA by hydrogen and hydrophobic bonds. The acidic and basic proteins are similar in amino acid composition except for the relative proportions of acidic to basic residues. The possible significance of this observation in relation to halophilism is discussed.