D
IPR007127

RNA polymerase sigma factor 70, region 1.1

InterPro entry
Short nameRNA_pol_sigma_70_r1_1
Overlapping
homologous
superfamilies
 

Description

The bacterial core RNA polymerase complex, which consists of five subunits, is sufficient for transcription elongation and termination but is unable to initiate transcription. Transcription initiation from promoter elements requires a sixth, dissociable subunit called a sigma factor, which reversibly associates with the core RNA polymerase complex to form a holoenzyme
[4]
. RNA polymerase recruits alternative sigma factors as a means of switching on specific regulons. Most bacteria express a multiplicity of sigma factors. Two of these factors, sigma-70 (gene rpoD), generally known as the major or primary sigma factor, and sigma-54 (gene rpoN or ntrA) direct the transcription of a wide variety of genes. The other sigma factors, known as alternative sigma factors, are required for the transcription of specific subsets of genes.

With regard to sequence similarity, sigma factors can be grouped into two classes, the sigma-54 and sigma-70 families. Sequence alignments of the sigma70 family members reveal four conserved regions that can be further divided into subregions eg. sub-region 2.2, which may be involved in the binding of the sigma factor to the core RNA polymerase; and sub-region 4.2, which seems to harbor a DNA-binding 'helix-turn-helix' motif involved in binding the conserved -35 region of promoters recognised by the major sigma factors
[5, 1]
.

The plastids of higher plants originating from an ancestral cyanobacterial endosymbiont also contain sigma factors that are encoded by a small family of nuclear genes. All plastid sigma factors belong to the superfamily of sigmaA/sigma70 and have sequences homologous to the conserved regions 1.2, 2, 3, and 4 of bacterial sigma factors
[6]
.

This entry represents Region 1.1 which modulates DNA binding by region 2 and 4 when sigma is unbound by the core RNA polymerase
[2, 3]
. Region 1.1 is also involved in promoter binding, it contains a basic patch on its surface which suggests to play an important role in DNA interaction to facilitate open promoter complex formation
[7]
.

References

1.The sigma 70 family: sequence conservation and evolutionary relationships. Lonetto M, Gribskov M, Gross CA. J. Bacteriol. 174, 3843-9, (1992). View articlePMID: 1597408

2.A mutation in region 1.1 of sigma70 affects promoter DNA binding by Escherichia coli RNA polymerase holoenzyme. Bowers CW, Dombroski AJ. EMBO J. 18, 709-16, (1999). View articlePMID: 9927430

3.Effects of amino acid substitutions at conserved and acidic residues within region 1.1 of Escherichia coli sigma(70). Bowers CW, McCracken A, Dombroski AJ. J. Bacteriol. 182, 221-4, (2000). View articlePMID: 10613885

4.Structure and function of bacterial sigma factors. Helmann JD, Chamberlin MJ. Annu. Rev. Biochem. 57, 839-72, (1988). View articlePMID: 3052291

5.Sigma factors from E. coli, B. subtilis, phage SP01, and phage T4 are homologous proteins. Gribskov M, Burgess RR. Nucleic Acids Res. 14, 6745-63, (1986). View articlePMID: 3092189

6.Plastid sigma factors: Their individual functions and regulation in transcription. Chi W, He B, Mao J, Jiang J, Zhang L. Biochim. Biophys. Acta 1847, 770-8, (2015). View articlePMID: 25596450

7.X-ray crystal structure of Escherichia coli RNA polymerase σ70 holoenzyme. Murakami KS. J Biol Chem 288, 9126-34, (2013). PMID: 23389035

GO terms

molecular function

cellular component

  • None
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