One Gene and Two Proteins: a Leaderless mRNA Supports the Translation of a Shorter Form of the <italic toggle="yes">Shigella</italic> VirF Regulator

ABSTRACT VirF, an AraC-like activator, is required to trigger a regulatory cascade that initiates the invasive program of Shigella spp., the etiological agents of bacillary dysentery in humans. VirF expression is activated upon entry into the host and depends on many environmental signals. Here, we...

Descripción completa

Guardado en:

Detalles Bibliográficos
Autores principales:	Maria Letizia Di Martino, Cédric Romilly, E. Gerhart H. Wagner, Bianca Colonna, Gianni Prosseda
Formato:	article
Lenguaje:	EN
Publicado:	American Society for Microbiology 2016
Materias:	Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/f04cf197d5c64f4887e3df87f436f9f3
Etiquetas:	Agregar Etiqueta Sin Etiquetas, Sea el primero en etiquetar este registro!

id	oai:doaj.org-article:f04cf197d5c64f4887e3df87f436f9f3
record_format	dspace
spelling	oai:doaj.org-article:f04cf197d5c64f4887e3df87f436f9f32021-11-15T15:50:15ZOne Gene and Two Proteins: a Leaderless mRNA Supports the Translation of a Shorter Form of the <italic toggle="yes">Shigella</italic> VirF Regulator10.1128/mBio.01860-162150-7511https://doaj.org/article/f04cf197d5c64f4887e3df87f436f9f32016-12-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.01860-16https://doaj.org/toc/2150-7511ABSTRACT VirF, an AraC-like activator, is required to trigger a regulatory cascade that initiates the invasive program of Shigella spp., the etiological agents of bacillary dysentery in humans. VirF expression is activated upon entry into the host and depends on many environmental signals. Here, we show that the virF mRNA is translated into two proteins, the major form, VirF30 (30 kDa), and the shorter VirF21 (21 kDa), lacking the N-terminal segment. By site-specific mutagenesis and toeprint analysis, we identified the translation start sites of VirF30 and VirF21 and showed that the two different forms of VirF arise from differential translation. Interestingly, in vitro and in vivo translation experiments showed that VirF21 is also translated from a leaderless mRNA (llmRNA) whose 5′ end is at position +309/+310, only 1 or 2 nucleotides upstream of the ATG84 start codon of VirF21. The llmRNA is transcribed from a gene-internal promoter, which we identified here. Functional analysis revealed that while VirF30 is responsible for activation of the virulence system, VirF21 negatively autoregulates virF expression itself. Since VirF21 modulates the intracellular VirF levels, this suggests that transcription of the llmRNA might occur when the onset of the virulence program is not required. We speculate that environmental cues, like stress conditions, may promote changes in virF mRNA transcription and preferential translation of llmRNA. IMPORTANCE Shigella spp. are a major cause of dysentery in humans. In bacteria of this genus, the activation of the invasive program involves a multitude of signals that act on all layers of the gene regulatory hierarchy. By controlling the essential genes for host cell invasion, VirF is the key regulator of the switch from the noninvasive to the invasive phenotype. Here, we show that the Shigella virF gene encodes two proteins of different sizes, VirF30 and VirF21, that are functionally distinct. The major form, VirF30, activates the genes necessary for virulence, whereas the minor VirF21, which shares the C-terminal two-thirds of VirF30, negatively autoregulates virF expression itself. VirF21 is transcribed from a newly identified gene-internal promoter and, moreover, is translated from an unusual leaderless mRNA. The identification of a new player in regulation adds complexity to the regulation of the Shigella invasive process and may help development of new therapies for shigellosis.Maria Letizia Di MartinoCédric RomillyE. Gerhart H. WagnerBianca ColonnaGianni ProssedaAmerican Society for MicrobiologyarticleMicrobiologyQR1-502ENmBio, Vol 7, Iss 6 (2016)
institution	DOAJ
collection	DOAJ
language	EN
topic	Microbiology QR1-502
spellingShingle	Microbiology QR1-502 Maria Letizia Di Martino Cédric Romilly E. Gerhart H. Wagner Bianca Colonna Gianni Prosseda One Gene and Two Proteins: a Leaderless mRNA Supports the Translation of a Shorter Form of the <italic toggle="yes">Shigella</italic> VirF Regulator
description	ABSTRACT VirF, an AraC-like activator, is required to trigger a regulatory cascade that initiates the invasive program of Shigella spp., the etiological agents of bacillary dysentery in humans. VirF expression is activated upon entry into the host and depends on many environmental signals. Here, we show that the virF mRNA is translated into two proteins, the major form, VirF30 (30 kDa), and the shorter VirF21 (21 kDa), lacking the N-terminal segment. By site-specific mutagenesis and toeprint analysis, we identified the translation start sites of VirF30 and VirF21 and showed that the two different forms of VirF arise from differential translation. Interestingly, in vitro and in vivo translation experiments showed that VirF21 is also translated from a leaderless mRNA (llmRNA) whose 5′ end is at position +309/+310, only 1 or 2 nucleotides upstream of the ATG84 start codon of VirF21. The llmRNA is transcribed from a gene-internal promoter, which we identified here. Functional analysis revealed that while VirF30 is responsible for activation of the virulence system, VirF21 negatively autoregulates virF expression itself. Since VirF21 modulates the intracellular VirF levels, this suggests that transcription of the llmRNA might occur when the onset of the virulence program is not required. We speculate that environmental cues, like stress conditions, may promote changes in virF mRNA transcription and preferential translation of llmRNA. IMPORTANCE Shigella spp. are a major cause of dysentery in humans. In bacteria of this genus, the activation of the invasive program involves a multitude of signals that act on all layers of the gene regulatory hierarchy. By controlling the essential genes for host cell invasion, VirF is the key regulator of the switch from the noninvasive to the invasive phenotype. Here, we show that the Shigella virF gene encodes two proteins of different sizes, VirF30 and VirF21, that are functionally distinct. The major form, VirF30, activates the genes necessary for virulence, whereas the minor VirF21, which shares the C-terminal two-thirds of VirF30, negatively autoregulates virF expression itself. VirF21 is transcribed from a newly identified gene-internal promoter and, moreover, is translated from an unusual leaderless mRNA. The identification of a new player in regulation adds complexity to the regulation of the Shigella invasive process and may help development of new therapies for shigellosis.
format	article
author	Maria Letizia Di Martino Cédric Romilly E. Gerhart H. Wagner Bianca Colonna Gianni Prosseda
author_facet	Maria Letizia Di Martino Cédric Romilly E. Gerhart H. Wagner Bianca Colonna Gianni Prosseda
author_sort	Maria Letizia Di Martino
title	One Gene and Two Proteins: a Leaderless mRNA Supports the Translation of a Shorter Form of the <italic toggle="yes">Shigella</italic> VirF Regulator
title_short	One Gene and Two Proteins: a Leaderless mRNA Supports the Translation of a Shorter Form of the <italic toggle="yes">Shigella</italic> VirF Regulator
title_full	One Gene and Two Proteins: a Leaderless mRNA Supports the Translation of a Shorter Form of the <italic toggle="yes">Shigella</italic> VirF Regulator
title_fullStr	One Gene and Two Proteins: a Leaderless mRNA Supports the Translation of a Shorter Form of the <italic toggle="yes">Shigella</italic> VirF Regulator
title_full_unstemmed	One Gene and Two Proteins: a Leaderless mRNA Supports the Translation of a Shorter Form of the <italic toggle="yes">Shigella</italic> VirF Regulator
title_sort	one gene and two proteins: a leaderless mrna supports the translation of a shorter form of the <italic toggle="yes">shigella</italic> virf regulator
publisher	American Society for Microbiology
publishDate	2016
url	https://doaj.org/article/f04cf197d5c64f4887e3df87f436f9f3
work_keys_str_mv	AT marialetiziadimartino onegeneandtwoproteinsaleaderlessmrnasupportsthetranslationofashorterformoftheitalictoggleyesshigellaitalicvirfregulator AT cedricromilly onegeneandtwoproteinsaleaderlessmrnasupportsthetranslationofashorterformoftheitalictoggleyesshigellaitalicvirfregulator AT egerharthwagner onegeneandtwoproteinsaleaderlessmrnasupportsthetranslationofashorterformoftheitalictoggleyesshigellaitalicvirfregulator AT biancacolonna onegeneandtwoproteinsaleaderlessmrnasupportsthetranslationofashorterformoftheitalictoggleyesshigellaitalicvirfregulator AT gianniprosseda onegeneandtwoproteinsaleaderlessmrnasupportsthetranslationofashorterformoftheitalictoggleyesshigellaitalicvirfregulator
_version_	1718427496666365952

One Gene and Two Proteins: a Leaderless mRNA Supports the Translation of a Shorter Form of the <italic toggle="yes">Shigella</italic> VirF Regulator

Ejemplares similares