Sigma Factor - Structure

Structure

Sigma factors have four main regions that are generally conserved:

N-terminus --------------------- C-terminus 1.1 2 3 4
Sigma70 region 1.1
Identifiers
Symbol Sigma70_r1_1
Pfam PF03979
InterPro IPR007127
Available protein structures:
Pfam structures
PDB RCSB PDB; PDBe
PDBsum structure summary
Sigma70 region 1.2
Crystal structure of Thermus aquaticus RNA polymerase sigma subunit fragment containing regions 1.2 to 3.1
Identifiers
Symbol Sigma70_r1_2
Pfam PF00140
InterPro IPR009042
PROSITE PDOC00592
SCOP 1sig
SUPERFAMILY 1sig
Available protein structures:
Pfam structures
PDB RCSB PDB; PDBe
PDBsum structure summary
Sigma70 region 2
Crystal structure of a sigma70 subunit fragment from Escherichia coli RNA polymerase
Identifiers
Symbol Sigma70_r2
Pfam PF04542
Pfam clan CL0123
InterPro IPR007627
PROSITE PDOC00592
SCOP 1sig
SUPERFAMILY 1sig
Available protein structures:
Pfam structures
PDB RCSB PDB; PDBe
PDBsum structure summary
Sigma70 region 3
Solution structure of sigma a region 4 from Thermotoga maritima
Identifiers
Symbol Sigma70_r3
Pfam PF04539
Pfam clan CL0123
InterPro IPR007624
SCOP 1ku2
SUPERFAMILY 1ku2
Available protein structures:
Pfam structures
PDB RCSB PDB; PDBe
PDBsum structure summary
Sigma70_r4
Solution structure of sigma a region 4 from Thermotoga maritima
Identifiers
Symbol Sigma70_r4
Pfam PF04545
Pfam clan CL0123
InterPro IPR007630
SCOP 1or7
SUPERFAMILY 1or7
Available protein structures:
Pfam structures
PDB RCSB PDB; PDBe
PDBsum structure summary
Sigma70 region 4.2
Crystal structure of Escherichia coli sigma e region 4 bound to its -35 element DNA
Identifiers
Symbol Sigma70_r4_2
Pfam PF08281
Pfam clan CL0123
InterPro IPR013249
SCOP 1or7
SUPERFAMILY 1or7
Available protein structures:
Pfam structures
PDB RCSB PDB; PDBe
PDBsum structure summary

The regions are further subdivided (e.g. 2 includes 2.1, 2.2, etc.)

  • Region 1.1 is found only in "primary sigma factors" (RpoD, RpoS in E.coli). It is involved in ensuring the sigma factor will only bind the promoter when it is complexed with the RNA polymerase.
  • Region 2.4 recognizes and binds to the promoter -10 element (formerly called "Pribnow box").
  • Region 4.2 recognizes and binds to the promoter -35 element.

One exception to this organization is in σ54-type sigma factors. Proteins homologous to σ54/RpoN are functional sigma factors, but they have significantly different primary amino acid sequences.

Read more about this topic:  Sigma Factor

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