What defines a sigma factor?

Sigma factors are subunits of all bacterial RNA polymerases that are responsible for determining the specificity of promoter DNA binding and efficient initiation of RNA synthesis (transcription). The first sigma factor discovered was the sigma70 (σ70) of the highly studied bacterium Escherichia coli.

How many sigma factors are there?

Sigma factors have also been discovered that are encoded by bacteriophage. By binding to core polymerase these proteins cause preferential transcription of phage genes. In the sporulating bacterium Bacillus subtilis, ten sigma factors have been discovered and characterized.

How is a sigma factor different from a transcription factor?

Abstract. Transcription is the first and most heavily regulated step in gene expression. Sigma (σ) factors are general transcription factors that reversibly bind RNA polymerase (RNAP) and mediate transcription of all genes in bacteria.

How are sigma factors regulated?

The sigma factors themselves are regulated by anti-sigma factors that bind and inhibit their cognate sigma factor, and ‘appropriators’ that deploy a particular sigma-associated RNA polymerase to a specific promoter class.

How does sigma factors recognize promoter?

In order to recognize their promoters, bacterial RNA polymerase enzymes require a specialized subunit called the sigma factor (0), which directly contacts the promoter sequence (Figure 9- 3.1). The complex formed by the sigma subunit with the remaining polymerase core subunits constitutes the bacterial holoenzyme.

Is a sigma factor a regulator?

The key regulator of general stress response in E. coli is the σ factor σS (σ38 or RpoS) (McCann et al., 1991; Battesti et al., 2011), which either directly or indirectly regulates about 10% of E. coli genes during the stationary phase (Weber et al., 2005).

What is the difference between sigma and Rho?

Answer: A sigma factor is a protein needed for initiation of RNA synthesis. It is a bacterial transcription initiation factor that enables specific binding of RNA polymerase to gene promoter. Rho is an ATP-dependent RNA-stimulated helicases that disrupt the nascent RNA-DNA complex.

What is a sigma factor in transcription?

Sigma factors (sigmas) are bacterial transcription factors that bind core RNA polymerase (RNAP) and direct transcription initiation at cognate promoter sites. However, most of their functions have been investigated in the context of RNAP.

What is sigma factor in transcription?

What is the primary function of the sigma factor?

A sigma factor (σ factor or specificity factor) is a protein needed for initiation of transcription in bacteria. It is a bacterial transcription initiation factor that enables specific binding of RNA polymerase (RNAP) to gene promoters. It is homologous to archaeal transcription factor B and to eukaryotic factor TFIIB.