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...

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Autores principales:	Morgan A. Feeney, Govind Chandra, Kim C. Findlay, Mark S. B. Paget, Mark J. Buttner
Formato:	article
Lenguaje:	EN
Publicado:	American Society for Microbiology 2017
Materias:	IF3 noncanonical start codon oxidative stress sigma factors translation initiation Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/b498b2ea2384475489dd613133b4c885
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spelling	oai:doaj.org-article:b498b2ea2384475489dd613133b4c8852021-11-15T15:51:28ZTranslational Control of the SigR-Directed Oxidative Stress Response in <italic toggle="yes">Streptomyces</italic> via IF3-Mediated Repression of a Noncanonical GTC Start Codon10.1128/mBio.00815-172150-7511https://doaj.org/article/b498b2ea2384475489dd613133b4c8852017-07-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.00815-17https://doaj.org/toc/2150-7511ABSTRACT 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.Morgan A. FeeneyGovind ChandraKim C. FindlayMark S. B. PagetMark J. ButtnerAmerican Society for MicrobiologyarticleIF3noncanonical start codonoxidative stresssigma factorstranslation initiationMicrobiologyQR1-502ENmBio, Vol 8, Iss 3 (2017)
institution	DOAJ
collection	DOAJ
language	EN
topic	IF3 noncanonical start codon oxidative stress sigma factors translation initiation Microbiology QR1-502
spellingShingle	IF3 noncanonical start codon oxidative stress sigma factors translation initiation Microbiology QR1-502 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
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.
format	article
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
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_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_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_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
publisher	American Society for Microbiology
publishDate	2017
url	https://doaj.org/article/b498b2ea2384475489dd613133b4c885
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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

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