The ability to transduce a signal across a membrane is a basic biological phenomenon that remains only poorly understood. Recently, a new mechanism of transduction across a membrane has been described. In this model proteases embedded within the membrane are triggered to catalyze the proteolytic release of membrane-anchored transcription factors. These novel proteases are polytopic membrane proteins with catalytic sites embedded in the lipid bilayer. To gain a deeper understanding into how information is transduced by these membrane-embedded proteases we are studying a signal transduction pathway that results in the proteolytic activation of a transcription factor involved in spore formation in the bacterium Bacillus subtilis. The ease with which genetic and biochemical analysis can be carried out in this organism makes this an ideal system to study this important class of proteases. The developmentally regulated transcription factor (sigmaK) is proteolytically released from the membrane by a membrane-embedded metalloprotease known as SpolVFB (referred to as B). B is activated by a signaling protease (IVB) located on the other side of the membrane. The specific hypothesis underlying the proposed research is that cell-cell signaling during sporulation is achieved by the action of IVB on one side of the membrane, which triggers the activity of the membrane-embedded metalloprotease B on the opposite side. We further hypothesize that additional regulatory proteins modulate this two-step proteolytic cleavage pathway, which results in transcription factor activation. Specifically, we propose to: 1. Determine how the IVB signaling molecule triggers B protease activity; 2. Characterize three regulators that modulate the timing of sigmaK activation; 3. Reconstitute and characterize B-mediated pro-sigmaK processing in vitro.
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