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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:

• σ³² (RpoH) - the Heat Shock Sigma Factor
• σ^E - the Extracytoplasmic sigma factor
• σ⁵⁴ (RpoN) - the Nitrogen responsive sigma factor
• σ^S (RpoS) - the stationary phase sigma factor