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Sigma Factors: Key Molecules in Physiology and Virulence

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  • Author: Riccardo Manganelli1
  • Editors: Graham F. Hatfull2, William R. Jacobs Jr.3
  • VIEW AFFILIATIONS HIDE AFFILIATIONS
    Affiliations: 1: Department of Molecular Medicine, University of Padova, Italy; 2: University of Pittsburgh, Pittsburgh, PA; 3: Howard Hughes Medical Institute, Albert Einstein College of Medicine, Bronx, NY
  • Source: microbiolspec January 2014 vol. 2 no. 1 doi:10.1128/microbiolspec.MGM2-0007-2013
  • Received 20 August 2013 Accepted 27 August 2013 Published 17 January 2014
  • R. Manganelli, riccardo.manganelli@unipd.it
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  • Abstract:

    Rapid adaptation to changing environments is one of the keys to the success of microorganisms. Since infection is a dynamic process, it is possible to predict that adaptation involves continuous modulation of its global transcriptional profile in response to the changing environment found in the human body. In the last 18 years several studies have stressed the role of sigma (σ) factors in this process. These are small interchangeable subunits of the RNA polymerase holoenzyme that are required for transcriptional initiation and that determine promoter specificity. The genome encodes 13 of these proteins, one of which—the principal σ factor σ—is essential. Of the other 12 σ factors, at least 6 are required for virulence. In this article we review our current knowledge of mycobacterial σ factors, their regulons, the complex mechanisms determining their regulation, and their roles in physiology and virulence.

  • Citation: Manganelli R. 2014. Sigma Factors: Key Molecules in Physiology and Virulence. Microbiol Spectrum 2(1):MGM2-0007-2013. doi:10.1128/microbiolspec.MGM2-0007-2013.

Key Concept Ranking

Gene Expression and Regulation
0.63629675
Ribosome Binding Site
0.48053363
Transcription Start Point
0.4586163
Sigma Factor SigmaB
0.43543774
Integral Membrane Proteins
0.42851818
0.63629675

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/content/journal/microbiolspec/10.1128/microbiolspec.MGM2-0007-2013
2014-01-17
2017-09-23

Abstract:

Rapid adaptation to changing environments is one of the keys to the success of microorganisms. Since infection is a dynamic process, it is possible to predict that adaptation involves continuous modulation of its global transcriptional profile in response to the changing environment found in the human body. In the last 18 years several studies have stressed the role of sigma (σ) factors in this process. These are small interchangeable subunits of the RNA polymerase holoenzyme that are required for transcriptional initiation and that determine promoter specificity. The genome encodes 13 of these proteins, one of which—the principal σ factor σ—is essential. Of the other 12 σ factors, at least 6 are required for virulence. In this article we review our current knowledge of mycobacterial σ factors, their regulons, the complex mechanisms determining their regulation, and their roles in physiology and virulence.

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FIGURE 1

Sequence of the region immediately upstream of the translational stat codon. White box indicates MprA binding sites. Gray letters indicate residues protected by MprA ( 55 , 56 ); light gray box indicates the putative σ-dependent promoter; dark gray box indicates the σ, σ, and σ putative promoter. −35 and −10 sequences are underlined. Transcriptional start points are shown in capital letters. Putative consensus sequences recognized by the four σ factors ( 53 ). Modified from reference 51 . doi:10.1128/microbiolspec.MGM2-0007-2013.f1.

Source: microbiolspec January 2014 vol. 2 no. 1 doi:10.1128/microbiolspec.MGM2-0007-2013
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FIGURE 2

Comparison of conserved domains and multidomains in Rv0093c and σ. zf-HC2, Putative zinc-finger found in some anti-σ factor proteins; COG5660, predicted integral membrane protein; PRK09649, RNA polymerase sigma factor σ; Sigma70_r2, σ region 2; Sigma70_r4, σ region 4. Alignments were performed at http://blast.ncbi.nlm.nih.gov/Blast.cgi. doi:10.1128/microbiolspec.MGM2-0007-2013.f2.

Source: microbiolspec January 2014 vol. 2 no. 1 doi:10.1128/microbiolspec.MGM2-0007-2013
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FIGURE 3

Alignment of σ (black) with Rv0093c (green) and σ (red). doi:10.1128/microbiolspec.MGM2-0007-2013.f3.

Source: microbiolspec January 2014 vol. 2 no. 1 doi:10.1128/microbiolspec.MGM2-0007-2013
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FIGURE 4

Sequence of the upstream region and of the first part of the coding region in containing the three promoters and the translational start sites of its three isoforms. Transcription start points are shown in capital letters, and putative −10 and −35 are underlined. MprA binding sites are boxed. Letters in gray indicate residues protected by MprA binding ( 55 , 56 ). Putative translation start codons are shown in boxed capital letters, while the putative ribosome binding site (RBS) is shown in boxed plain letters. The two arrows show the 9-bp duplication (ATCACGACC) found in the complex genomes. Modified from reference 83 . doi:10.1128/microbiolspec.MGM2-0007-2013.f4.

Source: microbiolspec January 2014 vol. 2 no. 1 doi:10.1128/microbiolspec.MGM2-0007-2013
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FIGURE 5

The σ network. Surface stress promotes PknB-dependent phosphorylation of RseA, leading to cleavage by ClpC1P2, which results in activation of the σ regulon. σ controls transcription of which in turn induces the regulon. An increase in ClpC1P2 levels leads to increased RseA degradation and a higher concentration of free σ (positive feedback loop) ( 86 ). σ also controls transcription of : Increased PPK1 levels raise PolyP concentration, which controls s transcription through MprB-dependent phosphorylation of MprA (positive feedback loop) ( 85 ). Also, a σ-dependent promoter drives transcription (positive feedback loop) ( 36 ). Finally, is subject to autoregulation (Chauhan and Gennaro, personal communication). Solid, dashed, and curved arrows represent transcriptional regulation, protein production, and catalytic reactions, respectively. Abstraction of feedback loops discussed in panel . Modified from reference 12 . doi:10.1128/microbiolspec.MGM2-0007-2013.f5.

Source: microbiolspec January 2014 vol. 2 no. 1 doi:10.1128/microbiolspec.MGM2-0007-2013
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FIGURE 6

Main regulatory network responsible for SigF regulation. Arrows indicate transcriptional regulation; truncated lines indicate posttranslational regulation. At least four other proteins—Rv0516c, Rv1364c, Rv1904, and RV2638—have been hypothesized to be involved in this network, but their role has not been elucidated yet. doi:10.1128/microbiolspec.MGM2-0007-2013.f6.

Source: microbiolspec January 2014 vol. 2 no. 1 doi:10.1128/microbiolspec.MGM2-0007-2013
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FIGURE 7

Regulatory network of σ factors. Arrows indicate transcriptional regulation; truncated lines indicate posttranslational regulation. The role of σ is still putative. SS, surface stress; LP, low phosphate; OS, oxidative stress. doi:10.1128/microbiolspec.MGM2-0007-2013.f7

Source: microbiolspec January 2014 vol. 2 no. 1 doi:10.1128/microbiolspec.MGM2-0007-2013
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Tables

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TABLE 1

σ factors

Source: microbiolspec January 2014 vol. 2 no. 1 doi:10.1128/microbiolspec.MGM2-0007-2013

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