Synthesis and breakdown of messenger RNA without protein synthesis.

Publisher Summary This chapter reviews the variety of possible mechanisms for the relaxed control phenomenon, without expressing the prejudices toward any of them It reviews that a single genetic locus in control of RNA synthesis as the “RC” locus and considered its effectiveness to be “relaxed” in all derivatives of the original mutant regardless of the amino acid deficiency imposed While all species of RNA accumulated in RC mutants, excess DNA synthesis seemed to be relatively minor during an absolute amino acid starvation It discusses the concept of relaxed control to the synthesis of DNA as well Since a significant synthesis of this macromolecule is observed only when a gradual depletion of the amino acid supply occurs, it is our view that its magnitude reflects the adequacy of the amino acid starvation rather than a genetically controlled relaxation Synthesis of DNA to the completion of its replication cycle in amino acid-starved strains that exhibit stringent control over RNA synthesis is also discussed New insights and new skills are needed in this field and the solicitation of these is the goal of this chapter It is hoped that amino acid auxotrophs of mammalian cells have become a reality, the question of the possible existence of a similar control phenomenon for RNA synthesis in mammalian cells may also be open to exploration

The relaxed control phenomenon.

Publisher Summary The concept of regulation of the formation of nucleic acids and proteins is recognized as a function of great physiological significance to cells. Regulation is defined as a process, which under the influence of environmental conditions, leads to variations in the quantity per cell of the macromolecule in question. A regulation can be general, simultaneously affecting all species within a class of macromolecules, or specific, when it affects only a single species. The specific type of regulation is mostly recognized as affecting proteins but by improvement for scoring specificities among transfer (t-RNA) and ribosomal (r-RNA) ribonucleic acid molecules, specific regulation can be also seen in these groups of macromolecules. Regulation can occur as a result of changes in the overall rate of synthesis of a macromolecule. However, with metabolically unstable molecules, it is noted that an observed regulation can also manifest variations in the rate of breakdown of these molecules.

Regulation of Nucleic Acid and Protein Formation in Bacteria

Messenger activity of nascent ribosomal RNA.

Amino acid deprivation of a “relaxed” auxotroph of Escherichia coli results in the accumulation of protein-deficient, immature ribosomes (“relaxed particles”). The ribonucleic acid (RNA) of these particles was shown to differ from mature ribosomal RNA in both sedimentation characteristics and in elution from columns of methylated albumin-keiselguhr. When relaxed particles were allowed to become converted to mature ribosomes, the unique properties of the RNA were lost, and this RNA became indistinguishable from mature RNA. The conversion of relaxed particles to ribosomes did not involve degradation and resynthesis of RNA. It is concluded that ribosomal RNA undergoes a configurational transition during ribosome development, and that this transition is not the result of changes in the primary structure of the RNA.

Structural transitions in ribonucleic acid during ribosome development.

1. When the methionine-requiring mutant 58-161 of Escherichia coli was starved of methionine, ribonucleic acid was made in the absence of protein synthesis. 2. Most of this ribonucleic acid was similar to that found in ribosomes but was contained in particles differing from ribosomes both in sedimentation coefficient and in chromatographic behaviour on diethylaminoethylcellulose. 3. When methionine was added to a starved culture, the ribonucleic acid synthesized during starvation was almost completely undegraded as growth resumed. A transient loss of 5-10% could be largely attributed to breakdown of messenger ribonucleic acid accumulated during starvation. 4. After the addition of methionine, ribosomes were formed from the particles, and during this period preferential synthesis of ribosomal protein took place. 5. It is suggested that under these conditions the direct synthesis of ribosomes from the particles may occur.

The synthesis of ribosomes by a mutant of escherichia coli.

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The synthesis of ribosomes by a mutant of escherichia coli.