Member database | PROSITE patterns |
PROSITE patterns type | conserved site |
Short name | SIGMA70_1 |
Description
Sigma factors
[3] are bacterial transcription initiation factors that promote
the attachment of the core RNA polymerase to specific initiation sites and are
then released. They alter the specificity of promoter recognition. 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. The sigma-70 family includes, in
addition to the primary sigma factor, a wide variety of sigma factors, some of
which are listed below:
- Bacillus sigma factors involved in the control of sporulation-specific
genes: sigma-E (sigE or spoIIGB), sigma-F (sigF or spoIIAC), sigma-G (sigG
or spoIIIG), sigma-H (sigH or spo0C) and sigma-K (sigK or
spoIVCB/spoIIIC).
- Escherichia coli and related bacteria sigma-32 (gene rpoH or htpR) involved
in the expression of heat shock genes.
- Escherichia coli and related bacteria sigma-27 (gene fliA) involved in
the expression of the flagellin gene.
- Escherichia coli sigma-S (gene rpoS or katF) which seems to be involved
in the expression of genes required for protection against external
stresses.
- Myxococcus xanthus sigma-B (sigB) which is essential for the late-stage
differentiation of that bacteria.
Alignments of the sigma-70 family permit the identification of four regions of
high conservation
[1][2]. Each of these four regions can in turn be subdivided
into a number of sub-regions. We developed signature patterns based on the two
best conserved sub-regions. The first pattern corresponds to sub-region 2.2;
the exact function of this sub-region is not known although it could be
involved in the binding of the sigma factor to the core RNA polymerase. The
second pattern corresponds to sub-region 4.2 which seems to harbor a DNA-
binding 'helix-turn-helix' motif involved in binding the conserved -35
region of promoters recognized by the major sigma factors. The second pattern
starts one residue before the N-terminal extremity of the HTH region and
ends six residues after its C-terminal extremity.
References
1.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
2.The sigma 70 family: sequence conservation and evolutionary relationships. Lonetto M, Gribskov M, Gross CA. J. Bacteriol. 174, 3843-9, (1992). View articlePMID: 1597408
3.Structure and function of bacterial sigma factors. Helmann JD, Chamberlin MJ. Annu. Rev. Biochem. 57, 839-72, (1988). View articlePMID: 3052291