-
WormBook : the Online Review of C.... Nov 2012About 70% of C. elegans mRNAs are trans-spliced to one of two 22 nucleotide spliced leaders. SL1 is used to trim off the 5' ends of pre-mRNAs and replace them with the... (Review)
Review
About 70% of C. elegans mRNAs are trans-spliced to one of two 22 nucleotide spliced leaders. SL1 is used to trim off the 5' ends of pre-mRNAs and replace them with the SL1 sequence. This processing event is very closely related to cis-splicing, or intron removal. The SL1 sequence is donated by a 100 nt small nuclear ribonucleoprotein particle (snRNP), the SL1 snRNP. This snRNP is structurally and functionally similar to the U snRNAs (U1, U2, U4, U5 and U6) that play key roles in intron removal and trans-splicing, except that the SL1 snRNP is consumed in the process. More than half of C. elegans pre-mRNAs are subject to SL1 trans-splicing, whereas ~30% are not trans-spliced. The remaining genes are trans-spliced by SL2, which is donated by a similar snRNP, the SL2 snRNP. SL2 recipients are all downstream genes in closely spaced gene clusters similar to bacterial operons. They are transcribed from a promoter at the 5' end of the cluster of between 2 and 8 genes. This transcription makes a polycistronic pre-mRNA that is co-transcriptionally processed by cleavage and polyadenylation at the 3' end of each gene, and this event is closely coupled to the SL2 trans-splicing event that occurs only ~100 nt further downstream. SL2 trans-splicing requires a sequence between the genes, the Ur element, that likely base pairs with the 5' splice site on the SL2 snRNP, in a manner analogous to the interaction between the 5' splice site in cis-splicing with the U1 snRNP. The key difference is that in trans-splicing, the snRNP contains the 5' splice site, whereas in cis-splicing the pre-mRNA does. Some operons, termed "hybrid operons", contain an additional promoter between two genes that can express the downstream gene or genes with a developmental profile that is different from that of the entire operon. The operons contain primarily genes required for rapid growth, including genes whose products are needed for mitochondrial function and the basic machinery of gene expression. Recent evidence suggests that RNA polymerase is poised at the promoters of growth genes, and operons allow more efficient recovery from growth-arrested states, resulting in reduction in the need for this cache of inactive RNA polymerase.
Topics: Animals; Caenorhabditis elegans; Evolution, Molecular; Genes, Helminth; Operon; RNA, Helminth; Ribonucleoproteins, Small Nuclear; Trans-Splicing
PubMed: 23175478
DOI: 10.1895/wormbook.1.5.2 -
Annual Review of Microbiology Oct 2021Bacterial protein synthesis rates have evolved to maintain preferred stoichiometries at striking precision, from the components of protein complexes to constituents of...
Bacterial protein synthesis rates have evolved to maintain preferred stoichiometries at striking precision, from the components of protein complexes to constituents of entire pathways. Setting relative protein production rates to be well within a factor of two requires concerted tuning of transcription, RNA turnover, and translation, allowing many potential regulatory strategies to achieve the preferred output. The last decade has seen a greatly expanded capacity for precise interrogation of each step of the central dogma genome-wide. Here, we summarize how these technologies have shaped the current understanding of diverse bacterial regulatory architectures underpinning stoichiometric protein synthesis. We focus on the emerging expanded view of bacterial operons, which encode diverse primary and secondary mRNA structures for tuning protein stoichiometry. Emphasis is placed on how quantitative tuning is achieved. We discuss the challenges and open questions in the application of quantitative, genome-wide methodologies to the problem of precise protein production.
Topics: Escherichia coli; Operon; Protein Biosynthesis; Proteins; RNA, Messenger; Transcription, Genetic
PubMed: 34343023
DOI: 10.1146/annurev-micro-041921-012646 -
Nucleic Acids Research Aug 2022CRISPR-Cas systems are bacterial defense systems for fighting against invaders such as bacteriophages and mobile genetic elements. To escape destruction by these...
CRISPR-Cas systems are bacterial defense systems for fighting against invaders such as bacteriophages and mobile genetic elements. To escape destruction by these bacterial immune systems, phages have co-evolved multiple anti-CRISPR (Acr) proteins, which inhibit CRISPR-Cas function. Many acr genes form an operon with genes encoding transcriptional regulators, called anti-CRISPR-associated (Aca) proteins. Aca10 is the most recently discovered Aca family that is encoded within an operon containing acrIC7 and acrIC6 in Pseudomonas citronellolis. Here, we report the high-resolution crystal structure of an Aca10 protein to unveil the molecular basis of transcriptional repressor role of Aca10 in the acrIC7-acrIC6-aca10 operon. We identified that Aca10 forms a dimer in solution, which is critical for binding specific DNA. We also showed that Aca10 directly recognizes a 21 bp palindromic sequence in the promoter of the acr operon. Finally, we revealed that R44 of Aca10 is a critical residue involved in the DNA binding, which likely results in a high degree of DNA bending.
Topics: Bacteria; Bacteriophages; CRISPR-Associated Proteins; CRISPR-Cas Systems; Operon; Transcription Factors
PubMed: 35920325
DOI: 10.1093/nar/gkac656 -
Molecular Microbiology Feb 1997Antitermination of transcription mediated by proteins interacting with mRNA sequences is described for nine operons/regulons. Eight of the systems are catabolic, while... (Review)
Review
Antitermination of transcription mediated by proteins interacting with mRNA sequences is described for nine operons/regulons. Eight of the systems are catabolic, while the ninth, the Klebsiella pneumoniae nas regulon, is involved in the assimilation of nitrate and nitrite. Six of the catabolic operons/regulons are found in Bacillus subtilis, one is found in Escherichia coli, and one in Pseudomonas aeruginosa. The antitermination system of five of the operons/regulons (E. coli blg, and sacPA, sacB, bgl, and lic from B. subtilis) are assigned to the bgl-sac family on the basis of extensive similarities with regard to antiterminator proteins and the sequences of the antiterminators. Other members of the bgl-sac family are the arb operon of Erwinia chrysanthemi and a presumed bgl operon of Lactococcus lactis. The antitermination systems of the other four operons/regulons (B. subtilis glp, B. subtilis hut, P. aeruginosa ami, and K. pneumoniae nas) seem to be unrelated both to the bgl-sac family and to each other. The antiterminator protein of the B. subtilis glp regulon has been found not only to cause antitermination but also to stabilize the resultant mRNA and to mediate glucose repression. If other antiterminator proteins, and antitermination factors, also prove to have additional functions, it will broaden the impact of antitermination as a means of controlling gene expression.
Topics: Bacillus subtilis; Bacterial Proteins; Escherichia coli; Gram-Negative Bacteria; Klebsiella pneumoniae; Operon; Protein Structure, Secondary; Pseudomonas aeruginosa; RNA, Messenger; RNA-Binding Proteins; Regulon; Transcription, Genetic
PubMed: 9044276
DOI: 10.1046/j.1365-2958.1997.d01-1867.x -
Microbial Cell Factories Jul 2022Functionally related genes in bacteria are often organized and transcribed as polycistronic transcriptional units. Examples are the fim operon, which codes for...
BACKGROUND
Functionally related genes in bacteria are often organized and transcribed as polycistronic transcriptional units. Examples are the fim operon, which codes for biogenesis of type 1 fimbriae in Escherichia coli, and the atp operon, which codes for the FoF1 ATP synthase. We tested the hypothesis that markerless polar mutations could be efficiently engineered using CRISPR/Cas12a in these loci.
RESULTS
Cas12a-mediated engineering of a terminator sequence inside the fimA gene occurred with efficiencies between 10 and 80% and depended on the terminator's sequence, whilst other types of mutations, such as a 97 bp deletion, occurred with 100% efficiency. Polar mutations using a terminator sequence were also engineered in the atp locus, which induced its transcriptional shutdown and produced identical phenotypes as a deletion of the whole atp locus (ΔatpIBEFHAGDC). Measuring the expression levels in the fim and atp loci showed that many supposedly non-polar mutants induced a significant polar effect on downstream genes. Finally, we also showed that transcriptional shutdown or deletion of the atp locus induces elevated levels of intracellular ATP during the exponential growth phase.
CONCLUSIONS
We conclude that Cas12a-mediated mutagenesis is an efficient simple system to generate polar mutants in E. coli. Different mutations were induced with varying degrees of efficiency, and we confirmed that all these mutations abolished the functions encoded in the fim and atp loci. We also conclude that it is difficult to predict which mutagenesis strategy will induce a polar effect in genes downstream of the mutation site. Furthermore the strategies described here can be used to manipulate the metabolism of E. coli as showcased by the increase in intracellular ATP in the markerless ΔatpIBEFHAGDC mutant.
Topics: Adenosine Triphosphate; CRISPR-Cas Systems; Escherichia coli; Gene Editing; Mutagenesis; Operon
PubMed: 35831865
DOI: 10.1186/s12934-022-01844-y -
Journal of the American Chemical Society Sep 2016Methanobactins (Mbns) are a growing family of ribosomally produced, post-translationally modified natural products. Characteristic nitrogen-containing heterocycles and...
Methanobactins (Mbns) are a growing family of ribosomally produced, post-translationally modified natural products. Characteristic nitrogen-containing heterocycles and neighboring thioamides allow these compounds to bind copper with high affinity. Genome mining has enabled the identification of Mbn operons in bacterial genomes and the prediction of diverse Mbn structures from operon content and precursor peptide sequence. Here we report the characterization of Mbn from Methylosinus (Ms.) species (sp.) LW4. The peptide backbone is distinct from all previously characterized Mbns, and the post-translational modifications correspond precisely to those predicted on the basis of the Ms. sp. LW4 Mbn operon. Thus, prediction based on genome analysis combined with isolation and structural characterization represents a phylogenetic approach to finding diverse Mbns and elucidating their biosynthetic pathways.
Topics: Imidazoles; Methylosinus; Oligopeptides; Operon; Protein Processing, Post-Translational
PubMed: 27527063
DOI: 10.1021/jacs.6b06821 -
Nucleic Acids Research Oct 2022CRISPR-Cas systems are adaptive immune systems in bacteria and archaea that provide resistance against phages and other mobile genetic elements. To fight against...
CRISPR-Cas systems are adaptive immune systems in bacteria and archaea that provide resistance against phages and other mobile genetic elements. To fight against CRISPR-Cas systems, phages and archaeal viruses encode anti-CRISPR (Acr) proteins that inhibit CRISPR-Cas systems. The expression of acr genes is controlled by anti-CRISPR-associated (Aca) proteins encoded within acr-aca operons. AcrIF24 is a recently identified Acr that inhibits the type I-F CRISPR-Cas system. Interestingly, AcrIF24 was predicted to be a dual-function Acr and Aca. Here, we elucidated the crystal structure of AcrIF24 from Pseudomonas aeruginosa and identified its operator sequence within the regulated acr-aca operon promoter. The structure of AcrIF24 has a novel domain composition, with wing, head and body domains. The body domain is responsible for recognition of promoter DNA for Aca regulatory activity. We also revealed that AcrIF24 directly bound to type I-F Cascade, specifically to Cas7 via its head domain as part of its Acr mechanism. Our results provide new molecular insights into the mechanism of a dual functional Acr-Aca protein.
Topics: CRISPR-Cas Systems; CRISPR-Associated Proteins; Bacteriophages; Pseudomonas aeruginosa; Operon
PubMed: 36243977
DOI: 10.1093/nar/gkac880 -
Nucleic Acids Research Feb 2022Operons are a hallmark of the genomic and regulatory architecture of prokaryotes. However, the mechanism by which two genes placed far apart gradually come close and...
Operons are a hallmark of the genomic and regulatory architecture of prokaryotes. However, the mechanism by which two genes placed far apart gradually come close and form operons remains to be elucidated. Here, we propose a new model of the origin of operons: Mobile genetic elements called insertion sequences can facilitate the formation of operons by consecutive insertion-deletion-excision reactions. This mechanism barely leaves traces of insertion sequences and thus difficult to detect in nature. In this study, as a proof-of-concept, we reproducibly demonstrated operon formation in the laboratory. The insertion sequence IS3 and the insertion sequence excision enhancer are genes found in a broad range of bacterial species. We introduced these genes into insertion sequence-less Escherichia coli and found that, supporting our hypothesis, the activity of the two genes altered the expression of genes surrounding IS3, closed a 2.7 kb gap between a pair of genes, and formed new operons. This study shows how insertion sequences can facilitate the rapid formation of operons through locally increasing the structural mutation rates and highlights how coevolution with mobile elements may shape the organization of prokaryotic genomes and gene regulation.
Topics: Catalysis; DNA Transposable Elements; Escherichia coli; Operon; Prokaryotic Cells
PubMed: 35066585
DOI: 10.1093/nar/gkac004 -
Briefings in Bioinformatics Sep 2008For most organisms, computational operon predictions are the only source of genome-wide operon information. Operon prediction methods described in literature are based... (Review)
Review
For most organisms, computational operon predictions are the only source of genome-wide operon information. Operon prediction methods described in literature are based on (a combination of) the following five criteria: (i) intergenic distance, (ii) conserved gene clusters, (iii) functional relation, (iv) sequence elements and (v) experimental evidence. The performance estimates of operon predictions reported in literature cannot directly be compared due to differences in methods and data used in these studies. Here, we survey the current status of operon prediction methods. Based on a comparison of the performance of operon predictions on Escherichia coli and Bacillus subtilis we conclude that there is still room for improvement. We expect that existing and newly generated genomics and transcriptomics data will further improve accuracy of operon prediction methods.
Topics: Algorithms; Base Sequence; Chromosome Mapping; Computer Simulation; Models, Genetic; Molecular Sequence Data; Operon; Sequence Alignment; Sequence Analysis, DNA; Software
PubMed: 18420711
DOI: 10.1093/bib/bbn019 -
Nucleic Acids Research Jan 2012The Prokaryotic Operon DataBase (ProOpDB, http://operons.ibt.unam.mx/OperonPredictor) constitutes one of the most precise and complete repositories of operon predictions...
The Prokaryotic Operon DataBase (ProOpDB, http://operons.ibt.unam.mx/OperonPredictor) constitutes one of the most precise and complete repositories of operon predictions now available. Using our novel and highly accurate operon identification algorithm, we have predicted the operon structures of more than 1200 prokaryotic genomes. ProOpDB offers diverse alternatives by which a set of operon predictions can be retrieved including: (i) organism name, (ii) metabolic pathways, as defined by the KEGG database, (iii) gene orthology, as defined by the COG database, (iv) conserved protein domains, as defined by the Pfam database, (v) reference gene and (vi) reference operon, among others. In order to limit the operon output to non-redundant organisms, ProOpDB offers an efficient method to select the most representative organisms based on a precompiled phylogenetic distances matrix. In addition, the ProOpDB operon predictions are used directly as the input data of our Gene Context Tool to visualize their genomic context and retrieve the sequence of their corresponding 5' regulatory regions, as well as the nucleotide or amino acid sequences of their genes.
Topics: Bacteria; Bacterial Proteins; Databases, Genetic; Internet; Metabolic Networks and Pathways; Operon; Phylogeny; Protein Structure, Tertiary
PubMed: 22096236
DOI: 10.1093/nar/gkr1020