Control of sigma factor activity during Bacillus subtilis sporulation.
When starved, Bacillus subtilis undergoes asymmetric division to produce two cell types with different fates. The larger mother cell engulfs the smaller forespore, then nurtures it and, eventually, lyses to release a dormant, environmentally resistant spore. Driving these changes is a programme of transcriptional gene regulation. At the heart of the programme are sigma factors, which become active at different times, some only in one cell type or the other, and each directing RNA polymerase to transcribe a different set of genes. The activity of each sigma factor in the cascade is carefully regulated by multiple mechanisms. In some cases, novel proteins control both sigma factor activity and morphogenesis, co-ordinating the programme of gene expression with morphological change. These bifunctional proteins, as well as other proteins involved in sigma factor activation, and even precursors of sigma factors themselves, are targeted to critical locations, allowing the mother cell and forespore to communicate with each other and to co-ordinate their programmes of gene expression. This signalling can result in proteolytic sigma factor activation. Other mechanisms, such as an anti-sigma factor and, perhaps, proteolytic degradation, prevent sigma factors from becoming active in the wrong cell type. Accessory transcription factors modulate RNA polymerase activity at specific promoters. Negative feedback loops limit sigma factor production and facilitate the transition from one sigma factor to the next. Together, the mechanisms controlling sigma factor activity ensure that genes are expressed at the proper time and level in each cell type.
Kroos
L
L
Department of Biochemistry, Michigan State University, East Lansing 48824, USA. kroos@pilot.msu.edu
Zhang
B
B
Ichikawa
H
H
Yu
Y T
YT
D000255:Adenosine Triphosphate / Q000378:metabolism; D001412:Bacillus subtilis / Q000502:physiology*; D001426:Bacterial Proteins / Q000378:metabolism / Q000502:physiology; D004268:DNA-Binding Proteins / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism; D008954:Models, Biological; D012808:Sigma Factor / Q000502:physiology*; D013170:Spores / Q000502:physiology*; D013234:Stem Cells / Q000502:physiology; D014157:Transcription Factors / Q000502:physiology
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D008565:Membrane Proteins; D012808:Sigma Factor; C080950:Spo0A protein, Bacillus subtilis; C071977:SpoIIID protein, Bacillus; D014157:Transcription Factors; C092468:spoIIR protein, Bacillus subtilis; C088067:spoIV protein, Bacillus megaterium; C030069:spore-specific proteins, Bacillus; C074423:bofA protein, Bacillus subtilis; D000255:Adenosine Triphosphate