Sigma factor
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Sigma factor (σ factor) is a prokaryotic initiation factor that binds to RNA polymerase and promotes attachment to promoter sites on DNA.
Structure
Sigma factor has four main regions:
N----------C
1 2 3 4
- Region 1 regulates interaction with DNA.
- Region 2 binds RNAP and binds to the -10 promoter site.
- Region 4 binds to the -35 promoter site.
Specialised Sigma Factors
Developmental responses involve transcription of genes by RNAP containing specialised sigma factors.
E.coli sigma factors:
- sigma-32 (RpoH) - the Heat Shock Sigma Factor
- sigma-E - the Extracytoplasmic sigma factor
- sigma-54 (RpoN) - the Nitrogen responsive sigma factor
- sigma-s (RpoS) - the Starvation stress sigma factor