Stringent control of ribosomal protein gene expression in Escherichia coli

The regulation of the expression of ribosomal protein genes was examined during partial inhibition of tRNA aminoacylation in isogenic rel(+) and rel(-) strains of E. coli B carrying a temperature-sensitive mutation in valyl-tRNA synthetase (EC 6.1.1.9) gene. Measurements of the differential synthesis rate of ribosomal protein, alpha(r) (ribosomal protein synthesis rate/total protein synthesis rate), indicate that ribosomal protein synthesis is regulated directly or indirectly by availability of charged tRNA, and that the synthesis of ribosomal protein, like the synthesis of rRNA, is subject to the influence of the rel gene control system.

In vitro synthesis of ribosomal proteins directed by Escherichia coli DNA

In vitro synthesis of a number of E. coli 30S ribosomal proteins has been demonstrated in a cell-free system consisting of ribosomes, initiation factors, RNA polymerase, a fraction containing soluble enzymes and factors, and E. coli DNA. DNA-dependent synthesis of the following 30S proteins has been demonstrated: S4, S5, S7, S8, S9, S10, S13, S14, S16, S19, and S20.

Assembly of bacterial ribosomes

I have not mentioned the remarkable progress made mainly by Fellner and his co-workers (86) in the elucidation of the primary structure of rRNA's and by Wittmann and his co-workers (87) in determining the structure of several ribosomal proteins. Such knowledge of primary structures is certainly the basis of complete understanding of the structure of the ribosome. With the current progress in technology, complete elucidation of the primary structure of all the ribosomal components is probably a matter of time. As indicated in this article, a rough approximation of the three-dimensional structure of ribosomes is likely to emerge soon. Although not mentioned in this article, studies of ribosomes from higher organisms are also progressing. We must, therefore, consider what further studies should be conducted and what kinds of questions we would like to solve. Some groups of investigators aim to elucidate the complete three-dimensional structure of ribosomes and to find out how these complex cell organelles function; they hope to determine the conformational changes of many of the component molecules within the ribosome structure in response to external macromolecules and cofactors engaged in protein synthesis. Such knowledge will also be important in enabling us to understand the regulation of translation of genetic messages. Other groups of investigators aim to elucidate the complex series of events which originate in the transcription of the more than 60 genes and culminate in the formation of the specific structure of the organelle. Complete reproduction in vitro of all the assembly events that occur in vivo should not be difficult to achieve in principle. It should then become possible to study in vitro any factor regulating the biogenesis of the organelle. Although we do not know whether such studies would reveal any new fundamental principle that governs the complex circuits of interconnected macromolecular interactions, the achievement of such a complete in vitro system would represent a necessary step in the comprehensive understanding of biogenesis of organelles, and eventually, of the more complex behavior and genesis of cells (89).

Functional correspondence between 30S ribosomal proteins of Escherichia coli and Bacillus stearothermophilus

30S ribosomal proteins from Bacillus stearothermophilus (B. proteins) have been fractionated and characterized with respect to their ability to replace various E. coli 30S proteins (E. proteins) in the E. coli 30S ribosome reconstitution system. The functional counterparts of all the E. proteins, except S1, S6, S9, and S13, have been tested. In all cases, B. proteins can substitute for E. proteins. Several purified B. proteins are chemically different from their functionally homologous E. proteins. Five B. proteins are immunochemically related to E. proteins; this set includes two proteins that could not be tested in the reconstitution system (S9 and S13). Thus most, if not all, of the E. proteins have functionally equivalent counterparts among B. proteins, even though properties of the two ribosomes are different in several respects. These results suggest that the fundamental structural organization of ribosomes may be the same throughout prokaryotic organisms.