Engulfment-regulated proteolysis of SpoIIQ: evidence that dual checkpoints control K activity
During Bacillus subtilis sporulation, the engulfment checkpoint is thought to directly regulate late forespore transcription but to indirectly regulate late mother cell transcription, via the G-produced protease SpoIVB. We here demonstrate that SpoIIQ is subject to G-independent, but engulfment-dependent, proteolysis that depends on SpoIVB. Thus, SpoIVB produced before engulfment supports some SpoIVB-dependent events, suggesting that its activity or access to substrates must be regulated by engulfment. Furthermore, a mutation (bofA) that allows K to be active without G does not allow K activity in engulfment mutants, although the pro-K processing enzyme (SpoIVFB) is localized to the septum in engulfment mutants, suggesting that engulfment comprises a second checkpoint for K Finally, we find that SpoIIQ and another protein required for G activity (SpoIIIAH), which directly interact and assemble helical structures around the forespore, recruit the K-processing enzyme SpoIVFB to the forespore and these structures. We suggest that these foci serve a synapse-like role, allowing engulfment to simultaneously control both G and K, and integrating multiple checkpoints and signalling pathways.
Document Type: Research Article
Affiliations: Division of Biological Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0377, USA.
Publication date: 2005-10-01