Magnesium Starvation of Aerobacter aerogenes I. Changes in Nucleic Acid Composition
- 1 January 1967
- journal article
- research article
- Published by American Society for Microbiology in Journal of Bacteriology
- Vol. 93 (1), 334-+
- https://doi.org/10.1128/jb.93.1.334-344.1967
Abstract
Aerobacter aerogenes incubated in a medium containing all factors necessary for exponential growth except Mg++ continued to synthesize nucleic-acids and proteins for more than 70 hr. provided the major carbon source was in excess at all times. After 24 hr. of Mb++ starvation, deoxyribonucleic-acid content in the culture had increased 10-fold. In contrast, the viable-cell count increased only about threefold during the first few hours and then remained approximately constant for the subsequent 70 hr. After specified intervals of Mg++ starvation, extracts of the bacteria, or ribonucleic-acid (RNA) purified from them, was centrlfuged through gradients of sucrose to separate transfer RNA from ribosomal components. After correcting for losses, we obtained the following results. There was a progressive rise in the content of transfer RNA competent to accept amino-acids and during starvation it remained completely stable. In contrast, the contents of normally sedtmenting ribosomal RNA and ribosomal subunits (30 and 50S) remained approximately constant for more than 24 hr. This did not result from stability of ribo-somes made prior to starvation together with an inhibition of synthesis of new particles. Rather, rtbosomes were continually breaking down and being replaced by an equivalent number of new ones. The breakdown of ribosomes appeared to be sequentially ordered; polysomes yielded 70S monomers, which then gave 30 and 50S particles, and these disintegrated to smaller units and finally to acid-soluble products. Furthermore, the particles derived from breakdown do not appear to exchange with subparticles on the path of assembly. Thus, rlbosome decay was age-dependent and ribosomal RNA molecules had a minimal life expectancy of 90 mln; however, some survived much longer.This publication has 34 references indexed in Scilit:
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