Regulation of the Escherichia coli L10 Operon

Abstract

It is now clear that in Escherichia coli the synthesis of many of the components involved in transcription and translation are carefully regulated. For example, the expression of a number of these genes is under stringent control (Dennis and Nomura, 1974; Furano and Wittel, 1976), the mechanism by which bacteria, when starved for an amino acid, turn off the synthesis of ribosomal RNA, tRNA, and specific mRNAs. The ribosome represents a unique situation in that the synthesis of the three RNAs and 53 proteins that make up the E. coli ribosome is coordinately controlled (Kjeldgaard and Gausing, 1974). This occurs despite the fact that the ribosomal protein genes are contained in at least 16 different transcription units. Another example is the synthesis of RNA polymerase. The genes for the four subunits are located on three different transcription units, but the Cell can carefully regulate the synthesis of this critical enzyme. It is of interest that the three transcription units containing the genes for the subunits of RNA polymerase also contain one or more genes for ribosomal proteins. Our laboratory has been interested in how E. coli regulates the synthesis of RNA polymerase and ribosomal proteins, and the present report will summarize studies on the L10 operon (also referred to as the β operon, or L10 transcription unit). This operon contains the genes for ribosomal proteins L10 and LI2 as well as the genes for the β and β’ subunits of RNA polymerase (Fig. 44.1).