Engulfment-regulated proteolysis of SpoIIQ: evidence that dual checkpoints control sigma activity

• Published in: Molecular microbiology Vol. 58; no. 1; p. 102
• Main Authors: Jiang, Xin, Rubio, Aileen, Chiba, Shinobu, Pogliano, Kit
• Format: Journal Article
• Language: English
• Published: England 01.10.2005
• Subjects: Bacillus subtilis - chemistry; Bacillus subtilis - physiology; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacterial Proteins - physiology; beta-Galactosidase - analysis; Endopeptidases - genetics; Endopeptidases - physiology; Genes, Reporter; Green Fluorescent Proteins - analysis; Membrane Proteins - genetics; Membrane Proteins - physiology; Protein Binding; Protein Transport - genetics; Protein Transport - physiology; Repressor Proteins - physiology; Sigma Factor - metabolism; Spores, Bacterial - chemistry; Transcription Factors - physiology
• ISSN: 0950-382X
• DOI: 10.1111/j.1365-2958.2005.04811.x

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 sigmaG-produced protease SpoIVB. We here demonstrate that SpoIIQ is subject to sigmaG-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 sigmaK to be active without sigmaG does not allow sigmaK activity in engulfment mutants, although the pro-sigmaK processing enzyme (SpoIVFB) is localized to the septum in engulfment mutants, suggesting that engulfment comprises a second checkpoint for sigmaK Finally, we find that SpoIIQ and another protein required for sigmaG activity (SpoIIIAH), which directly interact and assemble helical structures around the forespore, recruit the sigmaK-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 sigmaG and sigmaK, and integrating multiple checkpoints and signalling pathways.