This project is devoted to defining the ways living cells coordinate metabolic pathways with growth. The system currently studied consists of the patways to isoleucine and valine in bacteria. These pathways provide good examples of both specific controls (related to isoleucine and valine biosynthesis) and general controls (related to growth rate and state of the cells). The current findings will eventually be related to more complex systems and to more complex life forms. It is proposed to examine the significance of the principal form of specific control of the one multicistronic (ilvGEDA) operon of the ilv gene cluster in Escherichia coli, attenuation of the leader transcript by comparison of its nucleotide sequence with that of other bacterioa and of mutants of E. coli exhibiting altered control. Such mutants will be selected following specific mutagenesis directed to the attenuator region itself carried on Lambdadilv-lac phages. It is also planned to study the factors regulating transcription of the leader transcript both in vivo and in vitro with strains and templates lacking attenuation control. The way a positive control element, mu, needed for induction of the isomero-reductase, generates its signal will be studied by observing whether it binds to DNA and, if so, """"""""footprinting"""""""" the bound region. The direction of transcription of ilvGrama will be examined by ilv-lac fusions and by hybridization of message to separated strands of DNA templates. The basis for non-coordinate expression of the ilv operon will be studied by comparing the effect of location of ilv-lac fusions on coordination. The nature of control of the ilvBeta gene will be studied by determineation of nucleotide sequence and comparison of its leader with that of the ilv operon. The question of control of ilvBeta expression by other means will be examined in vivo and in vitro. The functioning of the pathways will also be studied in vitro by transcription and coupled transcription-translation experiments in an attempt to simulate the regulation observed in vivo. Finally, these findings will be applied in a rational way to the production of isoleucine, valine, and other amino acids by microbial processes.
