The synthesis of ribosomes is regulated in response to environment and development. A well-documented example of this is the growth rate control of ribosome synthesis in Escherichia coli. The goal of this project is to unravel the molecular mechanisms underlying this regulation. The information gained by this study should contribute to tbe understanding of regulation of cell growth. It will also elucidate mechanistic aspects of the processes of transcription termination and translation initiation. The E. coli ribosomal protein L-4, encoded by the third gene of the eleven gene S10 operon, is a multifunctional protein which serves as a ribosomal component and as a regulator of both transcription termination in the S10 leader and translation of the first gene of the operon. The purpose of the experiments proposed here is to provide a detailed molecular model for the two regulatory processes induced by excess L4. Currently it is known that transcription termination requires L4, NusA and certain leader sequences, but it is not clear how these components interact to prompt the RNA polymerase to terminate transcription at a specific site. Furthermore, it appears likely that additional component(s) are necessary for completion of the terrmination process. The mechanism for the translation control has not yet been elucidated. A proposed role of alternative secondary RNA structures will be tested and in vitro systems will be established for biochemical analysis of the translation regulation. Finally, L4 mutants will be analyzed to identify domains involved in the protein's various functions. Other experiments will explore new features of the regulation of the S10 operon: (i) possible upstream activating sequences, (ii) possible involvement of sequences outside of the promoter region in steady state growth control, and (iii) expression during stationary phase and out growth.