Engulfment-regulated proteolysis of SpoIIQ: evidence that dual checkpoints control sigma 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 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.
Jiang
Xin
X
Division of Biological Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0377, USA.
Rubio
Aileen
A
Chiba
Shinobu
S
Pogliano
Kit
K
D001412:Bacillus subtilis / Q000737:chemistry / Q000502:physiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010450:Endopeptidases / Q000235:genetics / Q000502:physiology; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000032:analysis; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D011485:Protein Binding; D021381:Protein Transport / Q000235:genetics / Q000502:physiology; D012097:Repressor Proteins / Q000502:physiology; D012808:Sigma Factor / Q000378:metabolism; D013171:Spores, Bacterial / Q000737:chemistry; D014157:Transcription Factors / Q000502:physiology*; D001616:beta-Galactosidase / Q000032:analysis
D001426:Bacterial Proteins; D008565:Membrane Proteins; D012097:Repressor Proteins; D012808:Sigma Factor; D014157:Transcription Factors; C112176:pro-sigmaK protein, Bacillus subtilis; C084190:sigma K; C030069:spore-specific proteins, Bacillus; C074423:bofA protein, Bacillus subtilis; C071441:spoIVFA protein, Bacillus subtilis; D049452:Green Fluorescent Proteins; D001616:beta-Galactosidase; D010450:Endopeptidases; C071442:spoIVFB protein, Bacillus subtilis