A sporulation membrane protein tethers the pro-ςK processing enzyme to its inhibitor and dictates its subcellular localization

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Abstract
The developmental transcription factor ςK is derived from the inactive precursor protein pro-ςK by regulated proteolysis during the process of sporulation in the bacteriumBacillus subtilis. The putative pro-ςK processing enzyme SpoIVFB is a member of a family of membrane-embedded metalloproteases and is held inactive by two other integral membrane proteins, SpoIVFA and BofA. Herein we show that the processing enzyme and its two regulators exist in a multimeric complex that localizes to the membrane surrounding the developing spore (the forespore). We further show that one of the regulators, SpoIVFA, plays a central role in both the formation of this complex and its subcellular localization. Evidence is presented in support of a model in which SpoIVFA acts as a platform for bringing BofA and SpoIVFB together, whereby BofA inhibits pro-ςK processing until a signal has been received from the forespore.