Short Open Reading Frames Research Articles

A Short Open Reading Frame Encompassing the MicroRNA173 Target Site Plays a Role in trans-Acting Small Interfering RNA Biogenesis.

trans-Acting small interfering RNAs (tasiRNAs) participate in the regulation of organ morphogenesis and determination of developmental timing in plants by down-regulating target genes through mRNA cleavage. The production of tasiRNAs is triggered by microRNA173 (miR173) and other specific microRNA-mediated cleavage of 5'-capped and 3'-polyadenylated primary TAS transcripts (pri-TASs). Although pri-TASs are not thought to encode functional proteins, they contain multiple short open reading frames (ORFs). For example, the primary TAS2 transcript (pri-TAS2) contains 11 short ORFs, and the third ORF from the 5' terminus (ORF3) encompasses the miR173 target site. Here, we show that nonsense mutations in ORF3 of pri-TAS2 upstream of the miR173 recognition site suppress tasiRNA accumulation and that ORF3 is translated in vitro. Glycerol gradient centrifugation analysis of Arabidopsis (Arabidopsis thaliana) plant extracts revealed that pri-TAS2 and its miR173-cleaved 5' and 3' fragments are fractionated together in the polysome fractions. These and previous results suggest that the 3' fragment of pri-TAS2, which is a source of tasiRNAs, forms a huge complex containing SGS3, miR173-programmed AGO1 RNA-induced silencing complex, the 5' fragment, and ribosomes. This complex overaccumulated, moderately accumulated, and did not accumulate in rdr6, sde5, and sgs3 mutants, respectively. The sgs3 sde5 and rdr6 sde5 double mutants showed phenotypes similar to those of sgs3 and sde5 single mutants, respectively, with regard to the TAS2-related RNA accumulation, suggesting that the complex is formed in an SGS3-dependent manner, somehow modified and stabilized by SDE5, and becomes competent for RDR6 action. Ribosomes in this complex likely play an important role in this process.

Expression of a second open reading frame present in the genome of tick-borne encephalitis virus strain Neudoerfl is not detectable in infected cells.

A short upstream open reading frame (uORF) was recently identified in the 5' untranslated region of some tick-borne encephalitis virus (TBEV) strains. However, it is not known if the peptide encoded by TBEV uORF (TuORF) is expressed in infected cells. Here we show that TuORF forms three phylogenetically separated clades which are typical of European, Siberian, and Far-Eastern TBEV subtypes. Analysis of selection pressure acting on the TuORF area showed that it is under positive selection pressure. Theoretically, TuORF may code for a short hydrophobic peptide embedded in a biological membrane. However, expression of TuORF was detectable neither by immunoblotting in tick and mammalian cell lines infected with TBEV nor by immunofluorescence in TBEV-infected mammalian cell lines. These results support the idea that TuORF is not expressed in TBEV-infected cell or expressed in undetectably low concentrations. Therefore we can assume that TuORF has either minor or no biological role in the TBEV life cycle.

High-Resolution Analysis of Coronavirus Gene Expression by RNA Sequencing and Ribosome Profiling

Members of the family Coronaviridae have the largest genomes of all RNA viruses, typically in the region of 30 kilobases. Several coronaviruses, such as Severe acute respiratory syndrome-related coronavirus (SARS-CoV) and Middle East respiratory syndrome-related coronavirus (MERS-CoV), are of medical importance, with high mortality rates and, in the case of SARS-CoV, significant pandemic potential. Other coronaviruses, such as Porcine epidemic diarrhea virus and Avian coronavirus, are important livestock pathogens. Ribosome profiling is a technique which exploits the capacity of the translating ribosome to protect around 30 nucleotides of mRNA from ribonuclease digestion. Ribosome-protected mRNA fragments are purified, subjected to deep sequencing and mapped back to the transcriptome to give a global “snap-shot” of translation. Parallel RNA sequencing allows normalization by transcript abundance. Here we apply ribosome profiling to cells infected with Murine coronavirus, mouse hepatitis virus, strain A59 (MHV-A59), a model coronavirus in the same genus as SARS-CoV and MERS-CoV. The data obtained allowed us to study the kinetics of virus transcription and translation with exquisite precision. We studied the timecourse of positive and negative-sense genomic and subgenomic viral RNA production and the relative translation efficiencies of the different virus ORFs. Virus mRNAs were not found to be translated more efficiently than host mRNAs; rather, virus translation dominates host translation at later time points due to high levels of virus transcripts. Triplet phasing of the profiling data allowed precise determination of translated reading frames and revealed several translated short open reading frames upstream of, or embedded within, known virus protein-coding regions. Ribosome pause sites were identified in the virus replicase polyprotein pp1a ORF and investigated experimentally. Contrary to expectations, ribosomes were not found to pause at the ribosomal frameshift site. To our knowledge this is the first application of ribosome profiling to an RNA virus.

Discovery and characterization of smORF-encoded bioactive polypeptides.

Analysis of genomes, transcriptomes and proteomes reveals the existence of hundreds to thousands of translated, yet non-annotated, short open reading frames (small ORFs or smORFs). The discovery of smORFs and their protein products, smORF-encoded polypeptides (SEPs), points to a fundamental gap in our knowledge of protein-coding genes. Various studies have identified central roles for smORFs in metabolism, apoptosis and development. The discovery of these bioactive SEPs emphasizes the functional potential of this unexplored class of biomolecules. Here, we provide an overview of this emerging field and highlight the opportunities for chemical biology to answer fundamental questions about these novel genes. Such studies will provide new insights into the protein-coding potential of genomes and identify functional genes with roles in biology and disease.

Proteogenomic Discovery of a Small, Novel Protein in Yeast Reveals a Strategy for the Detection of Unannotated Short Open Reading Frames.

In recent years, proteomic data have contributed to genome annotation efforts, most notably in humans and mice, and spawned a field termed "proteogenomics". Yeast, in contrast with higher eukaryotes, has a small genome, which has lent itself to simpler ORF prediction. Despite this, continual advances in mass spectrometry suggest that proteomics should be able to improve genome annotation even in this well-characterized species. Here we applied a proteogenomics workflow to yeast to identify novel protein-coding genes. Specific databases were generated, from intergenic regions of the genome, which were then queried with MS/MS data. This suggested the existence of several putative novel ORFs of <100 codons, one of which we chose to validate. Synthetic peptides, RNA-Seq analysis, and evidence of evolutionary conservation allowed for the unequivocal definition of a new protein of 78 amino acids encoded on chromosome X, which we dub YJR107C-A. It encodes a new type of domain, which ab initio modeling suggests as predominantly α-helical. We show that this gene is nonessential for growth; however, deletion increases sensitivity to osmotic stress. Finally, from the above discovery process, we discuss a generalizable strategy for the identification of short ORFs and small proteins, many of which are likely to be undiscovered.

SORFs.org: a repository of small ORFs identified by ribosome profiling.

With the advent of ribosome profiling, a next generation sequencing technique providing a “snap-shot’’ of translated mRNA in a cell, many short open reading frames (sORFs) with ribosomal activity were identified. Follow-up studies revealed the existence of functional peptides, so-called micropeptides, translated from these ‘sORFs’, indicating a new class of bio-active peptides. Over the last few years, several micropeptides exhibiting important cellular functions were discovered. However, ribosome occupancy does not necessarily imply an actual function of the translated peptide, leading to the development of various tools assessing the coding potential of sORFs. Here, we introduce sORFs.org (http://www.sorfs.org), a novel database for sORFs identified using ribosome profiling. Starting from ribosome profiling, sORFs.org identifies sORFs, incorporates state-of-the-art tools and metrics and stores results in a public database. Two query interfaces are provided, a default one enabling quick lookup of sORFs and a BioMart interface providing advanced query and export possibilities. At present, sORFs.org harbors 263 354 sORFs that demonstrate ribosome occupancy, originating from three different cell lines: HCT116 (human), E14_mESC (mouse) and S2 (fruit fly). sORFs.org aims to provide an extensive sORFs database accessible to researchers with limited bioinformatics knowledge, thus enabling easy integration into personal projects.

The Bacterial Transcription Termination Factor Rho Coordinates Mg2 + Homeostasis with Translational Signals

The bacterial protein Rho triggers transcription termination at the ends of many operons and when transcription and translation become uncoupled. In addition to these genome wide activities, Rho implements regulation of specific genes by dictating whether RNA polymerase terminates transcription within the 5′ leader region or continues into the downstream coding region. Here, we report that the Mg2+ channel gene corA in Salmonella enterica serovar Typhimurium, which was previously thought to be constitutively expressed, is regulated by a Rho-dependent terminator located within its 5′ leader region. We demonstrate that the unusually long and highly conserved corA leader mRNA can adopt two mutually exclusive conformations that determine whether or not Rho interacts with a Rho utilization site on the nascent RNA and thereby prevents transcription of the corA coding region. The RNA conformation that promotes Rho-dependent termination is favored by efficient translation of corL, a short open reading frame located within the corA leader. Thus, corA transcription is inversely coupled to corL translation. This mechanism resembles those governing expression of Salmonella's other two Mg2+ transport genes, suggesting that Rho links Mg2+ uptake to translational signals.

The role of the CCDC26 long noncoding RNA as a tumor suppressor

CCDC26 on chromosome 8q24 is considered to encode a long intergenic noncoding RNA because the short open reading frame within the mRNA transcribed from this gene is not conserved in any other species. Genome-wide analysis has revealed association of CCDC26 with certain tumors, for instance low-level glioma. Moreover, 1.5- to 2-fold amplifications of the whole or part of the CCDC26 genetic locus have been observed in pediatric acute myeloid leukemia patients. The CCDC26 gene is amplified in the HL-60 acute myeloid leukemia cell line, in which double minute chromosomes—abnormal tiny chromosomes—harbor the CCDC26 gene. We examined the function of CCDC26 by gene knock-down (KD) using short hairpin RNAs in K562 human myeloid leukemia cells. In four stable KD clones, CCDC26 expression was suppressed to 1% of its normal level by transcriptional gene suppression, not post-transcriptional suppression. The growth rates of these KD clones were reduced compared with those of control cells in media containing high serum concentrations. In contrast, in media containing much lower serum concentrations, the KD clones exhibited significantly higher growth rates than controls, and increased survival after serum withdrawal. Enhanced expression of a receptor tyrosine kinase, KIT , was detected in the KD clones, and treatment with ISCK03, a KIT inhibitor, eliminated their increased survival in the absence of serum. Therefore, CCDC26 seems to control myeloid leukemia cell growth through regulation of KIT expression. These observations suggest that CCDC26 is a tumor-suppressive long noncoding RNA because it suppresses the KIT oncogene that supports survival of cancer cells in the stem cell state.

Ribosome profiling reveals the what, when, where and how of protein synthesis.

Ribosome profiling, which involves the deep sequencing of ribosome-protected mRNA fragments, is a powerful tool for globally monitoring translation in vivo. The method has facilitated discovery of the regulation of gene expression underlying diverse and complex biological processes, of important aspects of the mechanism of protein synthesis, and even of new proteins, by providing a systematic approach for experimental annotation of coding regions. Here, we introduce the methodology of ribosome profiling and discuss examples in which this approach has been a key factor in guiding biological discovery, including its prominent role in identifying thousands of novel translated short open reading frames and alternative translation products.

A 5'-upstream short open reading frame encoded peptide regulates angiotensin type 1a receptor production and signalling via the β-arrestin pathway.

AUG sequences and short open reading frames are commonly present in the 5'-leader sequence of G protein-coupled receptor mRNAs. The presence of these upstream AUG sequences has been demonstrated to inhibit downstream receptor translation efficiency and, most recently, receptor signal transduction. A seven amino acid peptide encoded by a short open reading frame in exon 2 of the angiotensin type 1a receptor has been shown to inhibit non-G protein-coupled signalling of angiotensin II, without altering the classical G protein-coupled pathway activated by the ligand. This finding may lead to the development of a new class of angiotensin receptor antagonists with activities biased for one, but not all, of the signalling cascades activated by angiotensin II, which could have therapeutic implications for the myriad hormones and neurotransmitters that signal through G protein-coupled receptors.

Extensive identification and analysis of conserved small ORFs in animals.

BackgroundThere is increasing evidence that transcripts or transcript regions annotated as non-coding can harbor functional short open reading frames (sORFs). Loss-of-function experiments have identified essential developmental or physiological roles for a few of the encoded peptides (micropeptides), but genome-wide experimental or computational identification of functional sORFs remains challenging.ResultsHere, we expand our previously developed method and present results of an integrated computational pipeline for the identification of conserved sORFs in human, mouse, zebrafish, fruit fly, and the nematode C. elegans. Isolating specific conservation signatures indicative of purifying selection on amino acid (rather than nucleotide) sequence, we identify about 2,000 novel small ORFs located in the untranslated regions of canonical mRNAs or on transcripts annotated as non-coding. Predicted sORFs show stronger conservation signatures than those identified in previous studies and are sometimes conserved over large evolutionary distances. The encoded peptides have little homology to known proteins and are enriched in disordered regions and short linear interaction motifs. Published ribosome profiling data indicate translation of more than 100 novel sORFs, and mass spectrometry data provide evidence for more than 70 novel candidates.ConclusionsTaken together, we identify hundreds of previously unknown conserved sORFs in major model organisms. Our computational analyses and integration with experimental data show that these sORFs are expressed, often translated, and sometimes widely conserved, in some cases even between vertebrates and invertebrates. We thus provide an integrated resource of putatively functional micropeptides for functional validation in vivo.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-015-0742-x) contains supplementary material, which is available to authorized users.

Peptide-Induced Amyloid-Like Conformational Transitions in Proteins.

Changes in protein conformation can occur both as part of normal protein functioning and during disease pathogenesis. The most common conformational diseases are amyloidoses. Sometimes the development of a number of diseases which are not traditionally related to amyloidoses is associated with amyloid-like conformational transitions of proteins. Also, amyloid-like aggregates take part in normal physiological processes such as memorization and cell signaling. Several primary structural features of a protein are involved in conformational transitions. Also the protein proteolytic fragments can cause the conformational transitions in the protein. Short peptides which could be produced during the protein life cycle or which are encoded by short open reading frames can affect the protein conformation and function.

Abstract 022: A Short Open Reading Frame in the Angiotensin Type 1a Receptor 5' Leader Sequence Increases the Rate of Receptor Internalization

Background: We recently found that a seven amino acid peptide (PEP7) encoded within a short open reading frame (sORF) in exon 2 of the 5’ leader sequence (5'LS) of the angiotensin type 1a receptor (AT1aR) mRNA inhibits AT1aR-mediated activation of extracellular signal-regulated protein kinases 1 and 2 (Erk1/2) without having any effect on the AT1aR-inositol trisphosphate protein kinase C pathway. To investigate the mechanism by which PEP7 selectively inhibits the AT1aR-Erk1/2 signaling cascade, the start codon of the sORF was mutated at adenine -108 (A-108 to T-108) to create E1,2(-108T),3-AT1aR followed by cloning the E1,2,3-AT1aR and the mutant E1,2(-108T),3-AT1aR into the pEGFP-N2 plasmid. Methods: Human embryonic kidney 293 (HEK-293) cells were transfected with E1,2,3-AT1aR (intact sORF construct) or E1,2(-108T),3-AT1aR (disrupted sORF construct) by lipofectamine. Forty eight to seventy two hours later, live cell time lapse images were collected before and after treatment with Ang II (100 nM) using a TE300 Spinning disk laser scanning confocal microscope. Image analysis was performed using Velocity software. Results: Within 5 min of Ang II stimulation, punctae formed and moved throughout the cell membrane in cells transfected with both EGFP tagged receptors; however, even though the punctae represent the localized accumulation of identical AT1aR proteins, there were distinct differences in the intensity and time course of punctae. The rate of vesicle formation after Ang II treatment was markedly decreased by disrupting the PEP7 sORF [t1/2 (s): E1,2,3-AT1aR, 203s (N=21) vs E1,2(-108T),3-AT1aR, 328s (N=14); p&lt;0.0001]. Conclusion: The PEP7 sORF facilitates Ang II-induced AT1R internalization. These findings suggest that we have uncovered a new mechanism governing agonist-induced AT1aR cellular trafficking that could have implications not only for regulation of AT1aR signaling cascades but also for other trafficking proteins that contain an upstream sORF within their 5'LS.

The mitochondrial-derived peptide MOTS-c: a player in exceptional longevity?

Mitochondrial-derived peptides (MDP) are encoded by functional short open reading frames in the mitochondrial DNA (mtDNA). These include humanin, and the recently discovered mitochondrial open reading frame of the 12S rRNA-c (MOTS-c). Although more research is needed, we suggest that the m.1382A>C polymorphism located in the MOTS-c encoding mtDNA, which is specific for the Northeast Asian population, may be among the putative biological mechanisms explaining the high longevity of Japanese people.

MOLECULAR ANALYSIS OF THE COMPLETE GENOME SEQUENCE OF A TOBACCO ETCH VIRUS ISOLATE FROM CHINA

An isolate of Tobacco etch virus (TEV-Shaanxi) induces systemic mosaic and necrotic lines or etching in N. Tabacum and is transmitted by M. persicae more efficiently than A. gossypii. The complete genome of TEV-Shaanxi consists of 9,494 nucleotides, excluding the 3’poly (A) tail. It contains a single large open reading frame (ORF) coding for a polyprotein of 3,054 amino acids, with an AUG start codon and a UGA stop codon. The polyprotein encodes 10 proteins (P1, HC-Pro, P3, 6K1, CI, 6K2, NIa-VPg, NIa-Pro, Nib and CP), whose putative cleavage sites were identified by comparison with sequences of other known potyviruses. The identities of the 10 proteins of TEV-Shaanxi with other members of the genus Potyvirus were 30.5-62.7% and 29.4-68.8% at the nucleotide and amino acid levels, respectively. A short internal open reading frame, PIPO, was also highly conserved. TEV isolates whose sequences are available cluster into two groups which correspond with their host of origin.

Quality control of transcription start site selection by nonsense-mediated-mRNA decay.

Nonsense-mediated mRNA decay (NMD) is a translation-dependent RNA quality-control pathway targeting transcripts such as messenger RNAs harboring premature stop-codons or short upstream open reading frame (uORFs). Our transcription start sites (TSSs) analysis of Saccharomyces cerevisiae cells deficient for RNA degradation pathways revealed that about half of the pervasive transcripts are degraded by NMD, which provides a fail-safe mechanism to remove spurious transcripts that escaped degradation in the nucleus. Moreover, we found that the low specificity of RNA polymerase II TSSs selection generates, for 47% of the expressed genes, NMD-sensitive transcript isoforms carrying uORFs or starting downstream of the ATG START codon. Despite the low abundance of this last category of isoforms, their presence seems to constrain genomic sequences, as suggested by the significant bias against in-frame ATGs specifically found at the beginning of the corresponding genes and reflected by a depletion of methionines in the N-terminus of the encoded proteins.

The Discovery of Human sORF‐Encoded Polypeptides (SEPs) in Cell Lines and Tissue

The existence of nonannotated protein-coding human short open reading frames (sORFs) has been revealed through the direct detection of their sORF-encoded polypeptide (SEP) products. The discovery of novel SEPs increases the size of the genome and the proteome and provides insights into the molecular biology of mammalian cells, such as the prevalent usage of non- AUG start codons. Through modifications of the existing SEP-discovery workflow, we discover an additional 195 SEPs in K562 cells and extend this methodology to identify novel human SEPs in additional cell lines and human tissue for a final tally of 237 new SEPs. These results continue to expand the human genome and proteome and demonstrate that SEPs are a ubiquitous class of nonannotated polypeptides that require further investigation.

Primary transcripts of microRNAs encode regulatory peptides.

MicroRNAs (miRNAs) are small regulatory RNA molecules that inhibit the expression of specific target genes by binding to and cleaving their messenger RNAs or otherwise inhibiting their translation into proteins. miRNAs are transcribed as much larger primary transcripts (pri-miRNAs), the function of which is not fully understood. Here we show that plant pri-miRNAs contain short open reading frame sequences that encode regulatory peptides. The pri-miR171b of Medicago truncatula and the pri-miR165a of Arabidopsis thaliana produce peptides, which we term miPEP171b and miPEP165a, respectively, that enhance the accumulation of their corresponding mature miRNAs, resulting in downregulation of target genes involved in root development. The mechanism of miRNA-encoded peptide (miPEP) action involves increasing transcription of the pri-miRNA. Five other pri-miRNAs of A. thaliana and M. truncatula encode active miPEPs, suggesting that miPEPs are widespread throughout the plant kingdom. Synthetic miPEP171b and miPEP165a peptides applied to plants specifically trigger the accumulation of miR171b and miR165a, leading to reduction of lateral root development and stimulation of main root growth, respectively, suggesting that miPEPs might have agronomical applications.

The Mitochondrial-Derived Peptide MOTS-c Promotes Metabolic Homeostasis and Reduces Obesity and Insulin Resistance

Mitochondria are known to be functional organelles, but their role as a signaling unit is increasingly being appreciated. The identification of a short open reading frame (sORF) in the mitochondrial DNA (mtDNA) that encodes a signaling peptide, humanin, suggests the possible existence of additional sORFs in the mtDNA. Here we report a sORF within the mitochondrial 12S rRNA encoding a 16-amino-acid peptide named MOTS-c (mitochondrial open reading frame of the 12S rRNA-c) that regulates insulin sensitivity and metabolic homeostasis. Its primary target organ appears to be the skeletal muscle, and its cellular actions inhibit the folate cycle and its tethered de novo purine biosynthesis, leading to AMPK activation. MOTS-c treatment in mice prevented age-dependent and high-fat-diet-induced insulin resistance, as well as diet-induced obesity. These results suggest that mitochondria may actively regulate metabolic homeostasis at the cellular and organismal level via peptides encoded within their genome.

Erratum to: A putative cold shock protein-encoding gene isolated from Arthrobacter sp. A2-5 confers cold stress tolerance in yeast and plants

A putative cold shock protein gene, designated as ArCspA, was isolated from Arthrobacter sp. A2-5 extracted from soil at the South Pole. The ArCspA gene is 873 nucleotide bp long and includes a 207-bp short open reading frame (ORF) with 49.3–92% amino acid identity to peptide sequences of other bacterial cold shock proteins. Northern blot analysis revealed that ArCspA was highly expressed at low temperatures. Bio-functional analysis using ArCspA-overexpressed transgenic Saccharomyces cerevisiae showed that ArCspA conferred cold tolerance on yeast at low temperatures (15°C). We then developed an ArCspA-overexpressed transgenic tobacco line to determine whether ArCspA is also functional in plants. After cold treatment at −25°C for 90 min followed by recovery for 4 weeks at 25°C, 17 transgenic lines survived at a high rate (60.0%), whereas under the same treatment conditions, wild-type plants did not survive. We also found that progeny of transgenic tobacco plants subjected to freezing stress at −20°C had significantly higher seed germination ability than wild-type plants. These results clearly indicate that the ArCspA protein plays an important role in cold tolerance in both yeast and plants.