Implicated in the coupling of mother cell to forespore gene expression. Required for spore formation. Processes the pro-sigma K factor. Binds 1 zinc ion per subunit. Forms a complex with SpoIVFA and BofA localized in the mother-cell membrane surrounding the forespore. Transcribed during the stage II, but not required until stage IV of sporulation. Could be held inactive when BofA provides a fourth zinc ligand, preventing access to a water molecule and the sequence of pro sigma-K. Belongs to the peptidase M50B family.