scholarly journals Rho-Dependent Transcription Termination in the tnaOperon of Escherichia coli: Roles of the boxASequence and the rut Site

2000 ◽  
Vol 182 (14) ◽  
pp. 3981-3988 ◽  
Author(s):  
Kouacou Vincent Konan ◽  
Charles Yanofsky
Keyword(s):  
Escherichia Coli ◽  
Stop Codon ◽  
Transcription Termination ◽  
Point Mutations ◽  
Constitutive Expression ◽  
Peptide Sequence ◽  
Start Codon ◽  
Leader Peptide ◽  
Coding Region ◽  
High Level

ABSTRACT Expression of the tryptophanase (tna) operon ofEscherichia coli is regulated by catabolite repression and by tryptophan-induced transcription antitermination. Tryptophan induction prevents Rho-dependent transcription termination in the leader region of the operon. Induction requires translation of a 24-residue leader peptide-coding region, tnaC, containing a single, crucial Trp codon. Studies with a lacZ reporter construct lacking the tnaC-tnaA spacer region suggest that, in the presence of excess tryptophan, the TnaC leader peptide acts incis on the ribosome translating tnaC to inhibit its release. The stalled ribosome is thought to block Rho's access to the transcript. In this paper we examine the roles of theboxA sequence and the rut site in Rho-dependent termination. Deleting six nucleotides (CGC CCT) of boxA or introducing specific point mutations in boxA results in high-level constitutive expression. Some constitutive changes introduced in boxA do not change the TnaC peptide sequence. We confirm that deletion of the rut site results in constitutive expression. We also demonstrate that, in each constitutive construct, replacement of the tnaC start codon by a UAG stop codon reduces expression significantly, suggesting that constitutive expression requires translation of the tnaCcoding sequence. Addition of bicyclomycin, an inhibitor of Rho, to these UAG constructs increases expression, demonstrating that reduced expression is due to Rho action. Combining a boxA point mutation with rut site deletion results in constitutive expression comparable to that of a maximally induced operon. These results support the hypothesis that in the presence of tryptophan the ribosome translating tnaC blocks Rho's access to theboxA and rut sites, thereby preventing transcription termination.

scholarly journals Role of Ribosome Release in Regulation oftna Operon Expression in Escherichia coli

1999 ◽  
Vol 181 (5) ◽  
pp. 1530-1536 ◽  
Author(s):  
Kouacou Vincent Konan ◽  
Charles Yanofsky
Keyword(s):  
Escherichia Coli ◽  
Mutant Allele ◽  
Stop Codon ◽  
Leader Peptide ◽  
Coding Region ◽  
Reporter Construct ◽  
E Coli ◽  
Operon Expression ◽  
Basal Level Expression

ABSTRACT Expression of the degradative tryptophanase (tna) operon of Escherichia coli is regulated by catabolite repression and tryptophan-induced transcription antitermination. In cultures growing in the absence of added tryptophan, transcription of the structural genes of the tna operon is limited by Rho-dependent transcription termination in the leader region of the operon. Tryptophan induction prevents this Rho-dependent termination, and requires in-frame translation of a 24-residue leader peptide coding region, tnaC, that contains a single, crucial, Trp codon. Studies with a lacZ reporter construct lacking the spacer region between tnaC and the first major structural gene,tnaA, suggested that tryptophan induction might involvecis action by the TnaC leader peptide on the ribosome translating the tnaC coding region. The leader peptide was hypothesized to inhibit ribosome release at thetnaC stop codon, thereby blocking Rho’s access to the transcript. Regulatory studies with deletion constructs of thetna operon of Proteus vulgaris supported this interpretation. In the present study the putative role of thetnaC stop codon in tna operon regulation inE. coli was examined further by replacing the naturaltnaC stop codon, UGA, with UAG or UAA in atnaC-stop codon-tnaA′-′lacZ reporter construct. Basal level expression was reduced to 20 and 50% when the UGA stop codon was replaced by UAG or UAA, respectively, consistent with the finding that in E. coli translation terminates more efficiently at UAG and UAA than at UGA. Tryptophan induction was observed in strains with any of the stop codons. However, when UAG or UAA replaced UGA, the induced level of expression was also reduced to 15 and 50% of that obtained with UGA as the tnaC stop codon, respectively. Introduction of a mutant allele encoding a temperature-sensitive release factor 1, prfA1, increased basal level expression 60-fold when the tnaC stop codon was UAG and 3-fold when this stop codon was UAA; basal level expression was reduced by 50% in the construct with the natural stop codon, UGA. In strains with any of the three stop codons and the prfA1mutation, the induced levels of tna operon expression were virtually identical. The effects of tnaC stop codon identity on expression were also examined in the absence of Rho action, using tnaC-stop codon-′lacZ constructs that lack the tnaC-tnaA spacer region. Expression was low in the absence of tnaC stop codon suppression. In most cases, tryptophan addition resulted in about 50% inhibition of expression when UGA was replaced by UAG or UAA and the appropriate suppressor was present. Introduction of the prfA1 mutant allele increased expression of the suppressed construct with the UAG stop codon; tryptophan addition also resulted in ca. 50% inhibition. These findings provide additional evidence implicating the behavior of the ribosome translating tnaC in the regulation of tna operon expression.

scholarly journals The Evolutionarily Conserved Eukaryotic Arginine Attenuator Peptide Regulates the Movement of Ribosomes That Have Translated It

1998 ◽  
Vol 18 (12) ◽  
pp. 7528-7536 ◽  
Author(s):  
Zhong Wang ◽  
Peng Fang ◽  
Matthew S. Sachs
Keyword(s):  
Translational Control ◽  
Stop Codon ◽  
Firefly Luciferase ◽  
Upstream Open Reading Frame ◽  
Start Codon ◽  
Leader Peptide ◽  
Translation System ◽  
Coding Region ◽  
Reading Frame ◽  
Arginine Attenuator Peptide

ABSTRACT Translation of the upstream open reading frame (uORF) in the 5′ leader segment of the Neurospora crassa arg-2 mRNA causes reduced initiation at a downstream start codon when arginine is plentiful. Previous examination of this translational attenuation mechanism using a primer-extension inhibition (toeprint) assay in a homologous N. crassa cell-free translation system showed that arginine causes ribosomes to stall at the uORF termination codon. This stalling apparently regulates translation by preventing trailing scanning ribosomes from reaching the downstream start codon. Here we provide evidence that neither the distance between the uORF stop codon and the downstream initiation codon nor the nature of the stop codon used to terminate translation of the uORF-encoded arginine attenuator peptide (AAP) is important for regulation. Furthermore, translation of the AAP coding region regulates synthesis of the firefly luciferase polypeptide when it is fused directly at the N terminus of that polypeptide. In this case, the elongating ribosome stalls in response to Arg soon after it translates the AAP coding region. Regulation by this eukaryotic leader peptide thus appears to be exerted through a novel mechanism ofcis-acting translational control.

scholarly journals A Variation of the Translation Attenuation Model Can Explain the Inducible Regulation of the pBC16 Tetracycline Resistance Gene in Bacillus subtilis

2006 ◽  
Vol 188 (13) ◽  
pp. 4749-4758 ◽  
Author(s):  
Patricia B. Lodato ◽  
Elizabeth J. Rogers ◽  
Paul S. Lovett
Keyword(s):  
Secondary Structure ◽  
Binding Site ◽  
Resistance Gene ◽  
Stop Codon ◽  
Constitutive Expression ◽  
Ribosome Binding Site ◽  
Leader Peptide ◽  
Coding Region ◽  
Attenuation Model ◽  
Ribosome Binding

ABSTRACT Expression of the tet resistance gene from plasmid pBC16 is induced by the antibiotic tetracycline, and induction is independent of the native promoter for the gene. The nucleotide sequence at the 5′ end of the tet mRNA (the leader region) is predicted to assume a complex secondary structure that sequesters the ribosome binding site for the tet gene. A spontaneous, constitutively expressed tet gene variant contains a mutation predicted to provide the tet gene with a nonsequestered ribosome binding site. Lastly, comparable levels of tet mRNA can be demonstrated in tetracycline-induced and uninduced cells. These results are consistent with the idea that the pBC16 tet gene is regulated by translation attenuation, a model originally proposed to explain the inducible regulation of the cat and erm genes in gram-positive bacteria. As with inducible cat and erm genes, the pBC16 tet gene is preceded by a translated leader open reading frame consisting of a consensus ribosome binding site and an ATG initiation codon, followed by 19 sense codons and a stop codon. Mutations that block translation of cat and erm leaders prevent gene expression. In contrast, we show that mutations that block translation of the tet leader result in constitutive expression. We provide evidence that translation of the tet leader peptide coding region blocks tet expression by preventing the formation of a secondary-structure complex that would, in the absence of leader translation, expose the tet ribosome binding site. Tetracycline is proposed to induce tet by blocking or slowing leader translation. The results indicate that tet regulation is a variation of the translation attenuation model.

scholarly journals Translationskopplung via Termination-Reinitiation in Archaea und Bacteria

2021 ◽  
Author(s):  
◽  
Madeleine Huber
Keyword(s):  
Escherichia Coli ◽  
De Novo ◽  
Stop Codon ◽  
Haloferax Volcanii ◽  
Site Directed Mutagenesis ◽  
Start Codon ◽  
Directed Mutagenesis ◽  
Ribosome Display ◽  
E Coli

Operons wurden zuerst im Jahre 1961 beschrieben. Bis heute ist bekannt, dass die prokaryotischen Domänen Bacteria und Archaea Gene sowohl in monocistronischen als auch in bi- oder polycistronischen Transkripten exprimieren können. Häufig überlappen Gene sogar in ihren Sequenzen. Diese überlappenden Genpaare stehen nicht in Korrelation mit der Kompaktheit ihres Genoms. Das führt zu der Annahme, dass eine Art der Regulation vorliegt, welche weitere Proteine oder Gene nicht benötigt. Diese könnte eine gekoppelte Translation sein. Das bedeutet die Translation des stromabwärts-liegenden Gens ist abhängig von der Translation eines stromaufwärts-liegenden Gens. Diese Abhängigkeit kann zum Beispiel durch lang reichende Sekundärstrukturen entstehen, bei welchen Ribosomenbindestellen (RBS) des stromabwärts-liegenden Gens blockiert sind. Die de novo-Initiation am stromabwärts-liegenden Gen kann nur stattfinden, wenn das erste Gen translatiert wird und dabei die Sekundärstruktur an der RBS aufgeschmolzen wird. Für Genpaare in E. coli ist dieser Mechanismus gut untersucht. Ein anderes Beispiel für die Translationskopplung ist die Termination-Reinitiation, bei welcher ein Ribosom das erste Gen translatiert bis zum Stop-Codon, dort terminiert und direkt am stromabwärts-liegenden Start-Codon reinitiiert. Der Mechanismus via Termination-Reinitiation ist bis jetzt nur für eukaryontische Viren beschrieben worden. Im Gegensatz zu einer Kopplung über Sekundärstrukturen kommt es bei der Termination-Reinitiation am stromabwärts-liegenden Gen nicht zu einer de novo-Initiation sondern eine Reinitiation des Ribosoms findet statt. Diese Arbeit analysiert jene Art der Translationskopplung an Genen polycistronischer mRNAs in jeweils einem Modellorganismus als Vertreter der Archaea (Haloferax volcanii) und Bacteria (Escherichia coli). Hierfür wurden Reportergenvektoren erstellt, welche die überlappenden Genpaare an Reportergene fusionierten. Für diese Reportergene ist es möglich die Transkriptmenge zu quantifizieren sowie für die exprimierten Proteine Enzymassays durchgeführt werden können. Aus beiden Werten können Translationseffizienzen berechnet werden indem jeweils die Enzymaktivität pro Transkriptmenge ermittelt wird. Durch ein prämatures Stop-Codon in diesen Konstrukten ist es möglich zu unterscheiden ob es für die Translation des zweiten Gens essentiell ist, dass das Ribosom den Überlapp erreicht. Hiermit konnte für neun Genpaare in H. volcanii und vier Genpaare in E. coli gezeigt werden, dass eine Art der Kopplung stattfindet bei der es sich um eine Termination-Reinitiation handelt. Des Weiteren wurde analysiert, welche Auswirkungen intragene Shine-Dalgarno Sequenzen bei dem Event der Translationskopplung besitzen. Durch die Mutation solcher Motive und dem Vergleich der Translationseffizienzen der Konstrukte, mit und ohne einer SD Sequenz, wird für alle analysierten Genpaare beider Modellorganismen gezeigt, dass die SD Sequenz einen Einfluss auf diese Art der Kopplung hat. Zwischen den Genpaaren ist dieser Einfluss jedoch stark variabel. Weiterhin wurde der maximale Abstand zwischen zwei bicistronischen Genen untersucht, für welchen Translationskopplung via Termination-Reinitiation noch stattfinden kann. Hierfür wird durch site-directed mutagenesis jeweils ein prämatures Stop-Codon im stromaufwärts-liegenden Gen eingebracht, welches den intergenen Abstand zwischen den Genen in den jeweiligen Konstrukten vergrößert. Der Vergleich aller Konstrukte eines Genpaars zeigt in beiden Modellorganismen, dass die Termination-Reinitiation vom intergenen Abstand abhängig ist und die Translationseffizienz des stromabwärts-liegenden Reporters bereits ab 15 Nukleotiden Abstand abnimmt. Eine weitere Fragestellung dieser Arbeit war es, den genauen Mechanismus der Termination-Reinitiation zu analysieren. Für Ribosomen gibt es an der mRNA nach der Termination der Translation zwei Möglichkeiten: Entweder als 70S Ribosom bestehen zu bleiben und ein weiteres Start-Codon auf der mRNA zu suchen oder in seine beiden Untereinheiten zu dissoziieren, während die 50S Untereinheit die mRNA verlässt und die 30S Untereinheit über Wechselwirkungen an der mRNA verbleiben kann. Um diesen Mechanismus auf molekularer Ebene zu untersuchen, wird ein Versuchsablauf vorgestellt. Dieser ermöglicht das Event bei der Termination-Reinitiation in vitro zu analysieren. Eine Unterscheidung von 30S oder 70S Ribosomen bei der Reinitiation der Translation des stromabwärts-liegenden Gens wird ermöglicht. Die Idee dabei basiert auf einem ribosome display, bei welchem Translationskomplexe am Ende der Translation nicht in ihre Bestandteile zerfallen können, da die eingesetzte mRNA kein Stop-Codon enthält Der genaue Versuchsablauf, die benötigten Bestandteile sowie proof-of-principal Versuche sind in der Arbeit dargestellt und mögliche Optimierungen werden diskutiert.

A new species of the genus Tuberfemurus (Orthoptera: Tetrigoidea: Cladonotinae) with comments on the characters of mitochondrial genome

Zootaxa ◽  
2021 ◽  
Vol 5071 (3) ◽  
pp. 437-446
Author(s):  
MENG-QI WANG ◽  
YAO DENG ◽  
DE-LONG GUAN ◽  
BEN-YONG MAO ◽  
MIAO LI
Keyword(s):  
New Species ◽  
Mitochondrial Genome ◽  
Stop Codon ◽  
Complete Mitochondrial Genome ◽  
Hind Femur ◽  
Start Codon ◽  
Gene Arrangement ◽  
Coding Region ◽  
Phylogenetic Studies ◽  
A New Species

A new species, Tuberfemurus viridulus sp. nov. is described and illustrated with photographs. The new species is similar to T. torulisinotus Deng, 2019, but differs from the latter by broader vertex, invisible frontal costa in profile, distinctly truncate apex of hind pronotal process, and two large triangular projections on lower outer carinae of hind femur. An updated key to species of Tuberfemurus is provided. Simultaneously, the complete mitochondrial genome of Tuberfemurus viridulus sp. nov. is sequenced and analyzed. The total length of the assembled mitogenome is 15,060 bp with 37 typical mitochondrial genes and a non-coding region (A + T-rich region). The order and orientation of the gene arrangement pattern are identical to that of most Tetrigoidea species. All PCGs initiate with the standard start codon of ATN, except ATP6 with GAC and ND1 with TTG; and terminate with the complete stop codon (TAA/TAG) or with an incomplete T- codon. This data could provide the genome information available for Tetrigoidea and facilitate phylogenetic studies of related insects.  

scholarly journals Characterization of Two New Aminopeptidases in Escherichia coli

2005 ◽  
Vol 187 (11) ◽  
pp. 3671-3677 ◽  
Author(s):  
Yu Zheng ◽  
Richard J. Roberts ◽  
Simon Kasif ◽  
Chudi Guan
Keyword(s):  
Escherichia Coli ◽  
Stop Codon ◽  
Bacterial Species ◽  
Start Codon ◽  
Aminopeptidase Activity ◽  
Peptide Substrates ◽  
E Coli ◽  
Terminal Domain ◽  
Methionyl Aminopeptidase

ABSTRACT Two genes in the Escherichia coli genome, ypdE and ypdF, have been cloned and expressed, and their products have been purified. YpdF is shown to be a metalloenzyme with Xaa-Pro aminopeptidase activity and limited methionine aminopeptidase activity. Genes homologous to ypdF are widely distributed in bacterial species. The unique feature in the sequences of the products of these genes is a conserved C-terminal domain and a variable N-terminal domain. Full or partial deletion of the N terminus in YpdF leads to the loss of enzymatic activity. The conserved C-terminal domain is homologous to that of the methionyl aminopeptidase (encoded by map) in E. coli. However, YpdF and Map differ in their preference for the amino acid next to the initial methionine in the peptide substrates. The implication of this difference is discussed. ypdE is the immediate downstream gene of ypdF, and its start codon overlaps with the stop codon of ypdF by 1 base. YpdE is shown to be a metalloaminopeptidase and has a broad exoaminopeptidase activity.

scholarly journals Mitochondrial Translation of Saccharomyces cerevisiae COX2 mRNA Is Controlled by the Nucleotide Sequence Specifying the Pre-Cox2p Leader Peptide

2001 ◽  
Vol 21 (7) ◽  
pp. 2359-2372 ◽  
Author(s):  
Nathalie Bonnefoy ◽  
Nada Bsat ◽  
Thomas D. Fox
Keyword(s):  
Amino Acid ◽  
Mitochondrial Gene ◽  
Large Subunit ◽  
Point Mutations ◽  
Regulatory Elements ◽  
Leader Peptide ◽  
Mrna Sequence ◽  
Coding Region ◽  
Mitochondrial Translation

ABSTRACT The mitochondrial gene encoding yeast cytochrome oxidase subunit II (Cox2p) specifies a precursor protein with a 15-amino-acid leader peptide. Deletion of the entire leader peptide coding region is known to block Cox2p accumulation posttranscriptionally. Here, we examined in vivo the role of the pre-Cox2p leader peptide and the mRNA sequence that encodes it in the expression of a mitochondrial reporter gene,ARG8m , fused to the 91st codon ofCOX2. We found within the coding sequence antagonistic elements that control translation: the positive element includes sequences in the first 14 codons specifying the leader peptide, while the negative element appears to be within codons 15 to 91. Partial deletions, point mutations, and local frameshifts within the leader peptide coding region were placed in both thecox2::ARG8m reporter and inCOX2 itself. Surprisingly, the mRNA sequence of the first six codons specifying the leader peptide plays an important role in positively controlling translation, while the amino acid sequence of the leader peptide itself is relatively unconstrained. Two mutations that partially block translation can be suppressed by nearby sequence substitutions that weaken a predicted stem structure and by overproduction of either the COX2 mRNA-specific translational activator Pet111p or the large-subunit mitochondrial ribosomal protein MrpL36p. We propose that regulatory elements embedded in the translated COX2 mRNA sequence could play a role, together with trans-acting factors, in coupling regulated synthesis of nascent pre-Cox2p to its insertion in the mitochondrial inner membrane.

scholarly journals Transient Erythromycin Resistance Phenotype Associated with Peptidyl-tRNA Drop-Off on Early UGG and GGG Codons

2007 ◽  
Vol 189 (24) ◽  
pp. 8993-9000 ◽  
Author(s):  
Mirjana Mačvanin ◽  
Ernesto I. Gonzalez de Valdivia ◽  
David H. Ardell ◽  
Leif A. Isaksson
Keyword(s):  
Escherichia Coli ◽  
Amino Acid ◽  
Mrna Expression ◽  
Stop Codon ◽  
Peptide Sequence ◽  
Erythromycin Resistance ◽  
Resistance Phenotype ◽  
Peptide Moiety ◽  
Reporter Gene System ◽  
Peptide Product

ABSTRACT Expression of minigenes encoding tetra- or pentapeptides MXLX or MXLXV (E peptides), where X is a nonpolar amino acid, renders cells erythromycin resistant whereas expression of minigenes encoding tripeptide MXL does not. By using a 3A′ reporter gene system beginning with an E-peptide-encoding sequence, we asked whether the codons UGG and GGG, which are known to promote peptidyl-tRNA drop-off at early positions in mRNA, would result in a phenotype of erythromycin resistance if located after this sequence. We find that UGG or GGG, at either position +4 or +5, without a following stop codon, is associated with an erythromycin resistance phenotype upon gene induction. Our results suggest that, while a stop codon at +4 gives a tripeptide product (MIL) and erythromycin sensitivity, UGG or GGG codons at the same position give a tetrapeptide product (MILW or MILG) and phenotype of erythromycin resistance. Thus, the drop-off event on GGG or UGG codons occurs after incorporation of the corresponding amino acid into the growing peptide chain. Drop-off gives rise to a peptidyl-tRNA where the peptide moiety functionally mimics a minigene peptide product of the type previously associated with erythromycin resistance. Several genes in Escherichia coli fulfill the requirements of high mRNA expression and an E-peptide sequence followed by UGG or GGG at position +4 or +5 and should potentially be able to give an erythromycin resistance phenotype.

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