SpoIVB and CtpB Are Both Forespore Signals in the Activation of the Sporulation Transcription Factor σKinBacillus subtilis

• DOI: 10.1128/jb.00399-07
• Publication Date: 2007-06-09T04:56:59Z
• Authors: Nathalie Campo; David Z. Rudner
• Keywords: Spores, Bacterial; 0303 health sciences; 03 medical and health sciences; Bacterial Proteins; Serine Endopeptidases; Sigma Factor; Gene Expression Regulation, Bacterial; Bacillus subtilis; Signal Transduction; Transcription Factors

ABSTRACTThe proteolytic activation of the mother cell transcription factor pro-σKis controlled by a signal transduction pathway during sporulation in the bacteriumBacillus subtilis. The pro-σKprocessing enzyme SpoIVFB, a membrane-embedded metalloprotease, is held inactive by two other integral membrane proteins, SpoIVFA and BofA, in the mother cell membrane that surrounds the forespore. Two signaling serine proteases, SpoIVB and CtpB, trigger pro-σKprocessing by cleaving the regulatory protein SpoIVFA. The SpoIVB signal is absolutely required to activate pro-σKprocessing and is derived from the forespore compartment. CtpB is necessary for the proper timing of σKactivation and was thought to be a mother cell signal. Here, we show that thectpBgene is expressed in both the mother cell and forespore compartments but that synthesis in the forespore under the control of σGis both necessary and sufficient for the proper timing of pro-σKprocessing. We further show that SpoIVB cleaves CtpB in vitro and in vivo but that this cleavage does not appear to be necessary for CtpB activation. Thus, both signaling proteins are made in the forespore and independently target the same regulatory protein.