Abstract
In acetate buffer (pH 4.5) at 4°, Zn 2+, at a concentration of 0.2 M, fractionates the total RNA of Escherichia coli, prepared according to the hot phenol method, into rRNA's and tRNA. A similar fractionation is achieved with 0.1 M Cd 2+ at pH 5.0. The metal ion-insoluble and metal ion-soluble fractions were characterized by means of sucrose density gradient centrifugation, analytical ultracentrifugation, gel filtration on Sephadex G-150 and by measurement of amino acid-acceptor activity. The metal ion-insoluble fraction contained the two rRNA's, which had sedimentation coefficients of 21 S and 14 S, and was free from amino acid-acceptor activity. The metal ion-soluble fraction contained only tRNA, which had a sedimentation coefficient of 4 S, and had amino acid-acceptor activity which was comparable with that of “standard tRNA” obtained by gel filtration of total RNA. The melting curve of this fraction was indistinguishable from that of standard tRNA. Fractionation into rRNA's and tRNA could not be achieved with Cu 2+.
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