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J Bacteriol. 1972 March; 109(3): 1284-1294
Copyright © 1972 American Society for Microbiology. All Rights Reserved.

"Compartmentalization" of Escherichia coli Ribosomes and Ribonucleic Acid

¹ Department of Internal Medicine, Yale School of Medicine, New Haven, Connecticut 06510

ABSTRACT

Escherichia coli spheroplasts lysed by Brij 58 and deoxycholate were separated into supernatant (S) and membrane fractions by low-speed centrifugation. The membrane fraction was further divided into that which was releasable by deoxyribonuclease (fraction D) and that which was not (M). In the presence of 10^–2M Mg²⁺, the S, D, and M fractions contained, respectively, 60, 20, and 20% of the total cellular ribonucleic acid (RNA). Ribosomal and transfer RNA (rRNA, tRNA) were found in each fraction. The M + D fraction RNA was labeled more by a pulse label. Incorporation of uracil into the D fraction continued only as long as the uptake of exogenous uracil, suggesting that this was a major primary site of RNA synthesis. From pulse-labeled cells, each fraction contained precursor rRNA, and there was a 10S RNA in the M fraction. Ninety per cent of the ribosomal subunits and the ribosomal precursor particles, 26 and 43S, were in the S fraction. Precursor RNA (17S) was found in the 26S precursor particles. The D fraction contained 38% of the polysomes (this does not consider polysomes, if any, of the M fraction) which were labeled four times as much as the supernatant polysomes by a 1-min pulse of uracil. These results are interpreted to mean that new RNA is associated with a cytoplasmic membrane-RNA polymerase-DNA complex.