16 research outputs found
Découverte de nouveaux mécanismes d'actions des petits ARNs régulateurs bactériens
Le concept dâopĂ©ron, dĂ©fini en 1960 par Jacob et Monod comme Ă©tant un groupe de gĂšnes transcrits ensemble et dont les produits concourent Ă la rĂ©alisation d'une mĂȘme fonction physiologique, est restĂ© jusquâĂ tout rĂ©cemment pratiquement inchangĂ©. Selon ce modĂšle, toute rĂ©gulation gĂ©nĂ©tique a lieu au niveau transcriptionnel et est mĂ©diĂ©e par des facteurs protĂ©iques. Cependant, au cours de la derniĂšre dĂ©cennie, une rĂ©volution a eu lieu alors quâil fut dĂ©montrĂ© que des petites molĂ©cules d'ARN, appelĂ©s sRNAs (small RNAs), sont capables de rĂ©primer de maniĂšre post-transcriptionnelle lâexpression dâARN messagers (ARNm) chez les procaryotes. Leur mĂ©canisme d'action consiste gĂ©nĂ©ralement Ă inhiber la traduction d'un ARNm en compĂ©titionnant avec la liaison des ribosomes sur le site de liaison des ribosomes (SLR) situĂ© dans la rĂ©gion 5' non traduite dâun ARNm. Cette inhibition de la traduction sâaccompagne gĂ©nĂ©ralement d'une dĂ©gradation rapide de lâARNm cible. Les recherches que j'ai effectuĂ©es au cours de mes Ă©tudes de 2e et 3e cycle ont permis de dĂ©couvrir des mĂ©canismes alternatifs par lesquels les sRNAs peuvent rĂ©primer lâexpression dâARNm cibles. J'ai tout dâabord dĂ©montrĂ© que lâexpression du petit ARN RyhB lors d'une carence en fer entraĂźne la dĂ©gradation seulement partielle de lâARNm polycistronique iscRSUA. De plus, j'ai participĂ© Ă lâĂ©lucidation du mĂ©canisme de dĂ©gradation d'un ARNm par lâaction d'un sRNA. En effet, nous dĂ©montrons que le site de clivage de la RNase E se situe plusieurs centaines de nuclĂ©otides en aval dans le cadre de lecture de la cible et que l'arrĂȘt de la traduction n'est pas suffisant Ă lâobtention d'une dĂ©gradation rapide d'un ARNm cible. Finalement, j'ai caractĂ©risĂ© un nouveau mĂ©canisme par lequel un sRNA peut rĂ©primer la traduction dâun ARNm en sâappariant loin en amont du SLR par le recrutement de la protĂ©ine chaperon Hfq. Nous dĂ©montrons que c'est la protĂ©ine qui joue le rĂŽle principal dans la compĂ©tition avec les ribosomes
Com o diabo no corpo: os terrĂveis papagaios do Brasil colĂŽnia
Desde a Antiguidade, papagaios, periquitos e afins (Psittacidae) fascinaram os europeus por seu vivo colorido e uma notĂĄvel capacidade de interação com seres humanos. A descoberta do Novo Mundo nada faria alĂ©m de acrescentar novos elementos ao trĂĄfico de animais exĂłticos hĂĄ muito estabelecido pelos europeus com a Ăfrica e o Oriente. Sem possuir grandes mamĂferos, a AmĂ©rica tropical participaria desse comĂ©rcio com o que tinha de mais atrativo, essencialmente felinos, primatas e aves - em particular os papagaios, os quais eram embarcados em bom nĂșmero. Contudo, a julgar pelos documentos do Brasil colĂŽnia, esses volĂĄteis podiam inspirar muito pouca simpatia, pois nenhum outro animal - exceto as formigas - foi tantas vezes mencionado como praga para a agricultura. AlĂ©m disso, alguns psitĂĄcidas mostravam-se tĂŁo loquazes que inspiravam a sĂ©ria desconfiança de serem animais demonĂacos ou possessos, pois sĂł trĂȘs classes de entidades - anjos, homens e demĂŽnios - possuĂam o dom da palavra. Nos dias de hoje, vĂĄrios representantes dos Psittacidae ainda constituem uma ameaça para a agricultura, enquanto os indivĂduos muito faladores continuam despertando a suspeita de estarem possuĂdos pelo demĂŽnio. Transcendendo a mera curiosidade, essa crença exemplifica o quĂŁo intrincadas podem ser as relaçÔes do homem com o chamado âmundo naturalâ, revelando um universo mais amplo e multifacetado do que se poderia supor a princĂpio. Nesse sentido, a existĂȘncia de aves capazes de falar torna essa relação ainda mais complexa e evidencia que as dificuldades de estabelecer o limite entre o animal e o humano se estendem alĂ©m dos primatas e envolvem as mais inusitadas espĂ©cies zoolĂłgicas.Since ancient times, parrots and their allies (Psittacidae) have fascinated Europeans by their striking colors and notable ability to interact with human beings. The discovery of the New World added new species to the international exotic animal trade, which for many centuries had brought beasts to Europe from Africa and the Orient. Lacking large mammals, tropical America participated in this trade with its most appealing species, essentially felines, primates and birds - especially parrots - which were shipped in large numbers. It should be noted, however, that at times these birds were not well liked. In fact, according to documents from colonial Brazil, only the ants rank higher than parrots as the animals most often mentioned as agricultural pests. On the other hand, some of these birds were so chatty that people suspected them to be demonic or possessed animals, since only three classes of beings - angels, men and demons - have the ability to speak. Nowadays, several Psittacidae still constitute a threat to agriculture, and the suspicion that extremely talkative birds were demon possessed has also survived. More than a joke or a mere curiosity, this belief exemplifies how intricate manâs relationships with the ânatural worldâ may be. In this sense, the existence of birds that are able to speak adds a further twist to these relationships, demonstrating that the problem of establishing a boundary between the animal and the human does not only involve primates, but also includes some unusual zoological species
Découverte de nouveaux mécanismes d'actions des petits ARNs régulateurs bactériens
Le concept dâopĂ©ron, dĂ©fini en 1960 par Jacob et Monod comme Ă©tant un groupe de gĂšnes transcrits ensemble et dont les produits concourent Ă la rĂ©alisation d'une mĂȘme fonction physiologique, est restĂ© jusquâĂ tout rĂ©cemment pratiquement inchangĂ©. Selon ce modĂšle, toute rĂ©gulation gĂ©nĂ©tique a lieu au niveau transcriptionnel et est mĂ©diĂ©e par des facteurs protĂ©iques. Cependant, au cours de la derniĂšre dĂ©cennie, une rĂ©volution a eu lieu alors quâil fut dĂ©montrĂ© que des petites molĂ©cules d'ARN, appelĂ©s sRNAs (small RNAs), sont capables de rĂ©primer de maniĂšre post-transcriptionnelle lâexpression dâARN messagers (ARNm) chez les procaryotes. Leur mĂ©canisme d'action consiste gĂ©nĂ©ralement Ă inhiber la traduction d'un ARNm en compĂ©titionnant avec la liaison des ribosomes sur le site de liaison des ribosomes (SLR) situĂ© dans la rĂ©gion 5' non traduite dâun ARNm. Cette inhibition de la traduction sâaccompagne gĂ©nĂ©ralement d'une dĂ©gradation rapide de lâARNm cible. Les recherches que j'ai effectuĂ©es au cours de mes Ă©tudes de 2e et 3e cycle ont permis de dĂ©couvrir des mĂ©canismes alternatifs par lesquels les sRNAs peuvent rĂ©primer lâexpression dâARNm cibles. J'ai tout dâabord dĂ©montrĂ© que lâexpression du petit ARN RyhB lors d'une carence en fer entraĂźne la dĂ©gradation seulement partielle de lâARNm polycistronique iscRSUA. De plus, j'ai participĂ© Ă lâĂ©lucidation du mĂ©canisme de dĂ©gradation d'un ARNm par lâaction d'un sRNA. En effet, nous dĂ©montrons que le site de clivage de la RNase E se situe plusieurs centaines de nuclĂ©otides en aval dans le cadre de lecture de la cible et que l'arrĂȘt de la traduction n'est pas suffisant Ă lâobtention d'une dĂ©gradation rapide d'un ARNm cible. Finalement, j'ai caractĂ©risĂ© un nouveau mĂ©canisme par lequel un sRNA peut rĂ©primer la traduction dâun ARNm en sâappariant loin en amont du SLR par le recrutement de la protĂ©ine chaperon Hfq. Nous dĂ©montrons que c'est la protĂ©ine qui joue le rĂŽle principal dans la compĂ©tition avec les ribosomes
Small RNA-induced differential degradation of the polycistronic mRNA iscRSUA
Most polycistronic genes are expressed in a single transcript, in which each cistron produces a fixed amount of protein. In this report, we show the first example of differential degradation of a polycistronic gene induced by a small regulatory RNA (sRNA). Our data show that the iron-responsive sRNA, RyhB, binds to the second cistron of the polycistronic mRNA, iscRSUA, which encodes the necessary machinery for biosynthesis of FeâS clusters, and promotes the cleavage of the downstream iscSUA transcript. This cleavage gives rise to the remaining 5âČ-section of the transcript encoding IscR, a transcriptional regulator responsible for activation and repression of several genes depending on the cellular FeâS level. Our data indicate that the iscR transcript is stable and that translation is active. The stability of the iscR transcript depends on a 111-nucleotide long non-translated RNA section located between iscR and iscS, which forms a strong repetitive extragenic palindromic secondary structure and may protect against ribonucleases degradation. This novel regulation shows how sRNAs and mRNA structures can work together to modulate the transcriptional response to a specific stress
Small RNA-induced mRNA degradation achieved through both translation block and activated cleavage
Small RNA (sRNA)-induced mRNA degradation occurs through binding of an sRNA to a target mRNA with the concomitant action of the RNA degradosome, which induces an endoribonuclease E (RNase E)-dependent cleavage and degradation of the targeted mRNA. Because many sRNAs bind at the ribosome-binding site (RBS), it is possible that the resulting translation block is sufficient to promote the rapid degradation of the targeted mRNA. Contrary to this mechanism, we report here that the pairing of the sRNA RyhB to the target mRNA sodB initiates mRNA degradation even in the absence of translation on the mRNA target. Remarkably, even though it pairs at the RBS, the sRNA RyhB induces mRNA cleavage in vivo at a distal site located >350 nucleotides (nt) downstream from the RBS, ruling out local cleavage near the pairing site. Both the RNA chaperone Hfq and the RNA degradosome are required for efficient cleavage at the distal site. Thus, beyond translation initiation block, sRNA-induced mRNA cleavage requires several unexpected steps, many of which are determined by structural features of the target mRNA
Comparative study between transcriptionally- and translationally-acting adenine riboswitches reveals key differences in riboswitch regulatory mechanisms
Many bacterial mRNAs are regulated at the transcriptional or translational level by ligand-binding elements called riboswitches. Although they both bind adenine, the adenine riboswitches of Bacillus subtilis and Vibrio vulnificus differ by controlling transcription and translation, respectively. Here, we demonstrate that, beyond the obvious difference in transcriptional and translational modulation, both adenine riboswitches exhibit different ligand binding properties and appear to operate under different regulation regimes (kinetic versus thermodynamic). While the B. subtilis pbuE riboswitch fully depends on co-transcriptional binding of adenine to function, the V. vulnificus add riboswitch can bind to adenine after transcription is completed and still perform translation regulation. Further investigation demonstrates that the rate of transcription is critical for the B. subtilis pbuE riboswitch to perform efficiently, which is in agreement with a cotranscriptional regulation. Our results suggest that the nature of gene regulation control, that is transcription or translation, may have a high importance in riboswitch regulatory mechanisms
[Jeunes filles jouant avec un cygne ou Léda] : [estampe] / Peint par G: Lethiers Directeur de l'Ecole Française. // & Impériale des Beaux Arts à Rome. ; Dessiné par Aug.te Desnoyers ; & gravé sous sa direction // Par C: F: Noël ; & Massol.
Référence bibliographique : IFF19 DESNOYERS ou BOUCHER-DESNOYERS (Baron-Auguste-Gaspard-Louis), 1