The properties of certain S. coelicolor mutants blocked in the initiation of sporulation strongly suggest a direct connection between carbon-source catabolite repression, activation of antibiotic synthesis genes and morphological development. As a starting point for our investigation of how these complex metabolic and developmental processes interact, we have chosen to characterize in detail the regulatory mechanisms that control the transcriptional activity of the gal operon of S. coelicolor, a relatively simple transcription unit that is subject to both glucose-mediated catabolite repression and induction by galactose. It is proposed to: 1) purify and characterize the polymerase forms that transcribe gal, 2) define the cis-acting elements of the operon that determine its regulation, and 3) identify and isolate the trans-acting factors that mediate repression and induction. Members of the bacterial genus Streptomyces are of enormous industrial importance, since they are the source of about 80% of known antibiotics. These species are also of great interest from a genetic and developmental point of view because of the complexity of their life cycle. When deprived of nutrients, these bacteria undergo a complex morphological differentiation culminating in the production of dormant spores which can germinate when and where environmental conditions favor vegetative growth. The synthesis of antibiotics is intimately related to this developmental process, since it occurs during the development, and since many mutants blocked in development can't make antibiotics. It is clear that one of the signals for initiation of development is depletion of an easily assimilable carbon source, such as glucose. The mechanism whereby this signal is translated into a decision to begin the developmental process is not at all understood, but a working hypothesis is that this mechanism is related to one by which, during growth on glucose, genes whose activity is not essential under these conditions are shut off. The mechanism of this type of shutoff has yet to be investigated in detail in Streptomyces, but it is already clear that it is very different from analogous but much better understood mechanisms in other unrelated species of bacteria. This proposal to elucidate the mechanism of shutoff of a gene unnecessary for growth on glucose is of particular interest because of the central importance of this process in the complex life cycle of this bacterium (which also happens to be a species of great industrial importance), and is of general interest because it may establish new principles of control of gene activity.
