Diverse Mechanisms for Regulating Ribosomal Protein Synthesis in Escherichia coli

Abstract

This chapter describes the current knowledge of the organization and regulation of ribosomal genes, emphasizing recent work elucidating the molecular mechanisms regulating ribosomal protein synthesis and illustrating the diversity of these mechanisms. In E. coli, the small ribosomal subunit contains one rRNA molecule (16 S) and 21 proteins. The large subunit harbors two rRNA molecules (23 S and 5 S) and 34 proteins. All of the genes for these ribosomal components have been mapped on the E . coli chromosome. Furthermore, all but three of the r-protein genes have been sequenced. Because proteins are the most abundant cellular macromolecules, cell growth requires that a large fraction of the cell mass be devoted to the protein synthesis machinery— namely, the ribosomes and their ancillary factors. For example, in rapidly growing bacteria, ribosomes account for as much as 50% of cellular dry mass. Because ribosome formation commands such a large fraction of cellular resources, even minor adjustments in the rate of ribosome synthesis can have a major impact on the economy of the cell.