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| Signal Transduction, Differentiation, and DNA Transport in Bacillus subtilis |
| David A. Dubnau Ph.D. |
| Department of Microbiology |
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| Research Summary |
| We use genetic transformation in Bacillus subtilis to study two fundamental biological processes. The first is the mechanism of cellular differentiation in a simple system, resulting in two cell types. Before the end of exponential growth, about one out of ten cells becomes committed to entering the competence differentiation pathway. This commitment results from a signal transduction pathway, involving a phosphorylation cascade and the integration of signals reflecting the nutritional environment, population density, and growth stage. The determining step in commitment to competence is the transcription of comK, which encodes a competence-specific transcription factor. The transcription of comK is ComK-dependent, providing a positive feedback loop. The MecA protein binds to ComK, and targets ComK for degradation in the presence of ATP by ClpC, a prokaryotic proteosome-like complex. An upstream signal transduction cascade which responds to increased population density triggers the synthesis of ComS, which in turn prevents the binding of ComK by MecA. In the presence of ComS therefore, ComK is not degraded and triggers the explosive synthesis of more ComK. This regulated proteolysis system has been completely reconstructed in vitro using purified proteins. Synthesis is subject to additional regulatory inputs on the levels of transcription (both positive and negative control), all of which are under investigation. Many additional aspects of competence signaling and of the Mec system remain to be elucidated, particularly the mechanism that limits competence development to a subpopulation of cells. Also, competence results in a cell division arrest which is dependent on a protein known as ComGA. This aspect is also being actively pursued. The second process we investigate is the binding and transport of transforming DNA by the competent cell. A protein family has been identified and characterized which is responsible for elaborating a cell-surface localized DNA transport machine. We believe that an aqueous pore is formed by protein E3, through which DNA is transported by an ATP-driven DNA translocase (F1). Initial binding of transforming DNA to the cell surface occurs at E1, which we have shown to be a membrane-localized DNA-binding protein. Other proteins (G3-7) are also involved in DNA binding, possibly by aiding in the proper presentation of E3 at the cell surface.
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| Research Information |
Research Interests | Signal Transduction, Differentiation, and DNA Transport in Bacillus subtilis | Research Keywords | genetic competence, membrane proteins, signal transduction, transformation, transport |
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