Translational Control of the SigR-Directed Oxidative Stress Response in <italic toggle="yes">Streptomyces</italic> via IF3-Mediated Repression of a Noncanonical GTC Start Codon
ABSTRACT The major oxidative stress response in Streptomyces is controlled by the sigma factor SigR and its cognate antisigma factor RsrA, and SigR activity is tightly controlled through multiple mechanisms at both the transcriptional and posttranslational levels. Here we show that sigR has a highly...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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American Society for Microbiology
2017-07-01
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| Series: | mBio |
| Subjects: | |
| Online Access: | https://journals.asm.org/doi/10.1128/mBio.00815-17 |
| _version_ | 1819010166374268928 |
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| author | Morgan A. Feeney Govind Chandra Kim C. Findlay Mark S. B. Paget Mark J. Buttner |
| author_facet | Morgan A. Feeney Govind Chandra Kim C. Findlay Mark S. B. Paget Mark J. Buttner |
| author_sort | Morgan A. Feeney |
| collection | DOAJ |
| description | ABSTRACT The major oxidative stress response in Streptomyces is controlled by the sigma factor SigR and its cognate antisigma factor RsrA, and SigR activity is tightly controlled through multiple mechanisms at both the transcriptional and posttranslational levels. Here we show that sigR has a highly unusual GTC start codon and that this leads to another level of SigR regulation, in which SigR translation is repressed by translation initiation factor 3 (IF3). Changing the GTC to a canonical start codon causes SigR to be overproduced relative to RsrA, resulting in unregulated and constitutive expression of the SigR regulon. Similarly, introducing IF3* mutations that impair its ability to repress SigR translation has the same effect. Thus, the noncanonical GTC sigR start codon and its repression by IF3 are critical for the correct and proper functioning of the oxidative stress regulatory system. sigR and rsrA are cotranscribed and translationally coupled, and it had therefore been assumed that SigR and RsrA are produced in stoichiometric amounts. Here we show that RsrA can be transcribed and translated independently of SigR, present evidence that RsrA is normally produced in excess of SigR, and describe the factors that determine SigR-RsrA stoichiometry. IMPORTANCE In all sigma factor-antisigma factor regulatory switches, the relative abundance of the two proteins is critical to the proper functioning of the system. Many sigma-antisigma operons are cotranscribed and translationally coupled, leading to a generic assumption that the sigma and antisigma factors are produced in a fixed 1:1 ratio. In the case of sigR-rsrA, we show instead that the antisigma factor is produced in excess over the sigma factor, providing a buffer to prevent spurious release of sigma activity. This excess arises in part because sigR has an extremely rare noncanonical GTC start codon, and as a result, SigR translation initiation is repressed by IF3. This finding highlights the potential significance of noncanonical start codons, very few of which have been characterized experimentally. It also emphasizes the limitations of predicting start codons using bioinformatic approaches, which rely heavily on the assumption that ATG, GTG, and TTG are the only permissible start codons. |
| first_indexed | 2024-12-21T01:07:56Z |
| format | Article |
| id | doaj.art-b498b2ea2384475489dd613133b4c885 |
| institution | Directory Open Access Journal |
| issn | 2150-7511 |
| language | English |
| last_indexed | 2024-12-21T01:07:56Z |
| publishDate | 2017-07-01 |
| publisher | American Society for Microbiology |
| record_format | Article |
| series | mBio |
| spelling | doaj.art-b498b2ea2384475489dd613133b4c8852022-12-21T19:20:59ZengAmerican Society for MicrobiologymBio2150-75112017-07-018310.1128/mBio.00815-17Translational Control of the SigR-Directed Oxidative Stress Response in <italic toggle="yes">Streptomyces</italic> via IF3-Mediated Repression of a Noncanonical GTC Start CodonMorgan A. Feeney0Govind Chandra1Kim C. Findlay2Mark S. B. Paget3Mark J. Buttner4Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Norwich, United KingdomDepartment of Molecular Microbiology, John Innes Centre, Norwich Research Park, Norwich, United KingdomDepartment of Cell and Developmental Biology, John Innes Centre, Norwich Research Park, Norwich, United KingdomSchool of Life Sciences, University of Sussex, Brighton, United KingdomDepartment of Molecular Microbiology, John Innes Centre, Norwich Research Park, Norwich, United KingdomABSTRACT The major oxidative stress response in Streptomyces is controlled by the sigma factor SigR and its cognate antisigma factor RsrA, and SigR activity is tightly controlled through multiple mechanisms at both the transcriptional and posttranslational levels. Here we show that sigR has a highly unusual GTC start codon and that this leads to another level of SigR regulation, in which SigR translation is repressed by translation initiation factor 3 (IF3). Changing the GTC to a canonical start codon causes SigR to be overproduced relative to RsrA, resulting in unregulated and constitutive expression of the SigR regulon. Similarly, introducing IF3* mutations that impair its ability to repress SigR translation has the same effect. Thus, the noncanonical GTC sigR start codon and its repression by IF3 are critical for the correct and proper functioning of the oxidative stress regulatory system. sigR and rsrA are cotranscribed and translationally coupled, and it had therefore been assumed that SigR and RsrA are produced in stoichiometric amounts. Here we show that RsrA can be transcribed and translated independently of SigR, present evidence that RsrA is normally produced in excess of SigR, and describe the factors that determine SigR-RsrA stoichiometry. IMPORTANCE In all sigma factor-antisigma factor regulatory switches, the relative abundance of the two proteins is critical to the proper functioning of the system. Many sigma-antisigma operons are cotranscribed and translationally coupled, leading to a generic assumption that the sigma and antisigma factors are produced in a fixed 1:1 ratio. In the case of sigR-rsrA, we show instead that the antisigma factor is produced in excess over the sigma factor, providing a buffer to prevent spurious release of sigma activity. This excess arises in part because sigR has an extremely rare noncanonical GTC start codon, and as a result, SigR translation initiation is repressed by IF3. This finding highlights the potential significance of noncanonical start codons, very few of which have been characterized experimentally. It also emphasizes the limitations of predicting start codons using bioinformatic approaches, which rely heavily on the assumption that ATG, GTG, and TTG are the only permissible start codons.https://journals.asm.org/doi/10.1128/mBio.00815-17IF3noncanonical start codonoxidative stresssigma factorstranslation initiation |
| spellingShingle | Morgan A. Feeney Govind Chandra Kim C. Findlay Mark S. B. Paget Mark J. Buttner Translational Control of the SigR-Directed Oxidative Stress Response in <italic toggle="yes">Streptomyces</italic> via IF3-Mediated Repression of a Noncanonical GTC Start Codon mBio IF3 noncanonical start codon oxidative stress sigma factors translation initiation |
| title | Translational Control of the SigR-Directed Oxidative Stress Response in <italic toggle="yes">Streptomyces</italic> via IF3-Mediated Repression of a Noncanonical GTC Start Codon |
| title_full | Translational Control of the SigR-Directed Oxidative Stress Response in <italic toggle="yes">Streptomyces</italic> via IF3-Mediated Repression of a Noncanonical GTC Start Codon |
| title_fullStr | Translational Control of the SigR-Directed Oxidative Stress Response in <italic toggle="yes">Streptomyces</italic> via IF3-Mediated Repression of a Noncanonical GTC Start Codon |
| title_full_unstemmed | Translational Control of the SigR-Directed Oxidative Stress Response in <italic toggle="yes">Streptomyces</italic> via IF3-Mediated Repression of a Noncanonical GTC Start Codon |
| title_short | Translational Control of the SigR-Directed Oxidative Stress Response in <italic toggle="yes">Streptomyces</italic> via IF3-Mediated Repression of a Noncanonical GTC Start Codon |
| title_sort | translational control of the sigr directed oxidative stress response in italic toggle yes streptomyces italic via if3 mediated repression of a noncanonical gtc start codon |
| topic | IF3 noncanonical start codon oxidative stress sigma factors translation initiation |
| url | https://journals.asm.org/doi/10.1128/mBio.00815-17 |
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