Cell-cell signaling controls many processes in the biological world, including development, pathogenesis, growth, mating, and transformation. Signaling processes are often mediated by factors (e.g. hormones, pheromones, neurotransmitters) that are produced by some cells and sensed by others. In order to understand regulatory process involving cell-cell signaling, it is essential to identify the signaling molecules, determine how they are produced and sensed, and determine how the signals are transduced to elicit a regulatory response. The long term goal of this project is to understand how cell-cell signaling controls gene expression and differentiation in Bacillus subtilis. B. subtilis produces extracellular signaling molecules that are at least in part oligopeptides that accumulate in culture medium as cells grow to high density. These extracellular signaling peptides stimulate expression of genes needed for the development of genetic competence. Genetic competence in B. subtilis is the natural ability to be transformed by exogenous DNA and is an efficient means of genetic exchange.
Our aims are to purify and biochemically characterize the signaling molecules that induce competence gene expression and competence, to characterize how these extracellular signaling molecules are produced, to characterize the mechanisms by which cells sense and respond to these peptide factors, and to determine if the signaling factors involved in competence also affect sporulation. Included in these aims is to characterize the role of the spoOK (opp) operon in the cellular response to peptide signaling factors. Mutations in spoOK cause a defect in competence (and sporulation) and prevent cells from responding to the peptide signaling molecules that stimulate competence gene expression. spoOK encodes an oligopeptide permease that is a member of the large family of ATP-dependent transporters. This family of transport systems includes MDR, involved in multi-drug resistance, CFTR, the cystic fibrosis transmembrane regulator, and Hly, required for hemolysin export in some pathogenic bacteria. Also included in this family of transporters are a variety of permeases from bacteria that mediate uptake of many compounds, including histidine, maltose, phosphate, dipeptides, vitamin B 12, and iron. An important aim of this proposal is to determine how the oligopeptide Permease encoded by spoOK of B. subtilis is involved in controlling expression of competence genes. Our studies on differentiation in this relatively simple, experimentally accessible microbe should provide insights into general mechanisms of cell-cell signaling, signal transduction, and regulation of gene expression and differentiation.
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