Involved in the mediation of the intercompartmental coupling of pro-sigma K processing to events in the forespore. Inhibits SpoIVFB-processing activity until a signal has been received from the forespore. Could inhibit SpoIVFB metalloprotease activity by coordinating a zinc in the SpoIVFB active site, preventing access of a water molecule and the sequence of pro-sigma K, which are necessary for peptide bond hydrolysis to produce sigma-K. Forms a complex with SpoIVFA and SpoIVFB localized in the mother cell membrane surrounding the forespore.