ASSOCIATION OF 5S RIBONUCLEIC ACID TO 50S RIBOSOMAL SUBUNITS OF ESCHERICHIA COLI AND BACILLUS SUBTILIS

In confirmation of earlier results with Escherichia coli it has been demonstrated that all of the 5S ribonucleic acid (RNA) of Bacillus subtilis is accounted for by the presence of one 5S RNA bound to each 50S ribosomal subunit. Isolated 50S subunits from E. coli and B. subtilis were treated with CsCl, LiCl, or EDTA under a variety of conditions and the particles derived were assayed for the presence or absence of 5S RNA by polyacrylamide gel electrophoresis. Ribonucleo-protein particles, A particles, with a sedimentation coefficient of about 40 S, produced by banding ribosomes in a CsCl gradient in the presence of Mg2+, were deficient in protein but retained all of their 5S RNA. A′ particles, produced by treatment of ribosomes with CsCl at a lower Mg2+ concentration or by treatment with LiCl, contained even less protein and were devoid of 5S RNA. It was also possible to remove 5S RNA from 50S ribosomal subunits of E. coli by treatment with EDTA. This procedure produced conformational changes of the ribosomes without significant loss of protein. Experiments involving pulse labeling of E. coli with [3H]uridine gave indirect evidence for a pool of cold 5S RNA or precursor to 5S RNA. It was also shown that attachment of 5S RNA to ribosomal precursors of the mature 50S subunit occurs at a late stage of ribosome biosynthesis. © 1968, American Chemical Society. All rights reserved.