Short open reading frames (sORFs) and microproteins: an update on their identification and validation measures (original) (raw)
Related papers
sORFs.org: a repository of small ORFs identified by ribosome profiling
Nucleic Acids Research, 2015
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 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.
Author response: Extensive translation of small Open Reading Frames revealed by Poly-Ribo-Seq
Thousands of small Open Reading Frames (smORFs) with the potential to encode small peptides of fewer than 100 amino acids exist in our genomes. However, the number of smORFs actually translated, and their molecular and functional roles are still unclear. In this study, we present a genome-wide assessment of smORF translation by ribosomal profiling of polysomal fractions in Drosophila. We detect two types of smORFs bound by multiple ribosomes and thus undergoing productive translation. The 'longer' smORFs of around 80 amino acids resemble canonical proteins in translational metrics and conservation, and display a propensity to contain transmembrane motifs. The 'dwarf' smORFs are in general shorter (around 20 amino-acid long), are mostly found in 5′-UTRs and non-coding RNAs, are less well conserved, and have no bioinformatic indicators of peptide function. Our findings indicate that thousands of smORFs are translated in metazoan genomes, reinforcing the idea that smORFs are an abundant and fundamental genome component.
Extensive translation of small Open Reading Frames revealed by Poly-Ribo-Seq
eLife, 2014
Thousands of small Open Reading Frames (smORFs) with the potential to encode small peptides of fewer than 100 amino acids exist in our genomes. However, the number of smORFs actually translated, and their molecular and functional roles are still unclear. In this study, we present a genome-wide assessment of smORF translation by ribosomal profiling of polysomal fractions in Drosophila. We detect two types of smORFs bound by multiple ribosomes and thus undergoing productive translation. The ‘longer’ smORFs of around 80 amino acids resemble canonical proteins in translational metrics and conservation, and display a propensity to contain transmembrane motifs. The ‘dwarf’ smORFs are in general shorter (around 20 amino-acid long), are mostly found in 5′-UTRs and non-coding RNAs, are less well conserved, and have no bioinformatic indicators of peptide function. Our findings indicate that thousands of smORFs are translated in metazoan genomes, reinforcing the idea that smORFs are an abundan...
ABSTRACTRibosome profiling (Ribo-seq) has catalyzed a paradigm shift in our understanding of the translational ‘vocabulary’ of the human genome, discovering thousands of translated open reading frames (ORFs) within long non-coding RNAs and presumed untranslated regions of protein-coding genes. However, reference gene annotation projects have been circumspect in their incorporation of these ORFs due to uncertainties about their experimental reproducibility and physiological roles. Yet, it is indisputable that certain Ribo-seq ORFs make stable proteins, others mediate gene regulation, and many have medical implications. Ultimately, the absence of standardized ORF annotation has created a circular problem: while Ribo-seq ORFs remain unannotated by reference biological databases, this lack of characterisation will thwart research efforts examining their roles. Here, we outline the initial stages of a community-led effort supported by GENCODE / Ensembl, HGNC and UniProt to produce a cons...
PROTEOMICS
Short ORF-encoded peptides and small proteins in eukaryotes have been hiding in the shadow of large proteins for a long time. Recently, improved identifications in MS-based proteomics and ribosome profiling resulted in the detection of large numbers of small proteins. The variety of functions of small proteins is also emerging. It seems to be the right time to reflect on why small proteins remained invisible. In addition to the obvious technical challenge of detecting small proteins, they were mostly forgotten from annotations and they escaped detection because they were not sought. In this review, we identify conventions that need to be revisited, including the assumption that mature mRNAs carry only one coding sequence. The large-scale discovery of small proteins and of their functions will require changing some paradigms and undertaking the annotation of ORFs that are still largely perceived as irrelevant coding information compared to already annotated coding sequences.
De novo transcriptome assembly workflow v1
protocols.io, 2016
Protein-coding small open reading frames (smORFs) are emerging as an important class of genes, however, the coding capacity of smORFs in the human genome is unclear. By integrating de novo transcriptome assembly and Ribo-Seq, we confidently annotate thousands of novel translated smORFs in three human cell lines. We find that smORF translation prediction is noisier than for annotated coding sequences, underscoring the importance of analyzing multiple experiments and footprinting conditions. These smORFs are located within non-coding and antisense transcripts, the UTRs of mRNAs, and unannotated transcripts. Analysis of RNA levels and translation efficiency during cellular stress identifies regulated smORFs, providing an approach to select smORFs for further investigation. Sequence conservation and signatures of positive selection indicate that encoded microproteins are likely functional. Additionally, proteomics data from enriched human leukocyte antigen complexes validates the translation of hundreds of smORFs and positions them as a source of novel antigens. Thus, smORFs represent a significant number of important, yet unexplored human genes. .
Ribosomal profiling adds new coding sequences to the proteome
Biochemical Society transactions, 2015
Next generation sequencing (NGS) has enabled an in-depth look into genes, transcripts and their translation at the genomic scale. The application of NGS sequencing of ribosome footprints (Ribo-Seq) reveals translation with single nucleotide (nt) resolution, through the deep sequencing of ribosome-bound fragments (RBFs). Some results of Ribo-Seq challenge our understanding of the protein-coding potential of the genome. Earlier bioinformatic approaches had shown the presence of hundreds of thousands of putative small ORFs (smORFs) in eukaryotic genomes, but they had been largely ignored due to their large numbers and difficulty in determining their translation and function. Ribo-Seq has revealed that hundreds of putative smORFs within previously assumed long non-coding RNAs (lncRNAs) and UTRs of canonical mRNAs are associated with ribosomes, appearing to be translated. Here we review some of the approaches used to define translation within Ribo-Seq experiments and the challenges in de...
BMC Genomics, 2013
Background: It was long assumed that proteins are at least 100 amino acids (AAs) long. Moreover, the detection of short translation products (e.g. coded from small Open Reading Frames, sORFs) is very difficult as the short length makes it hard to distinguish true coding ORFs from ORFs occurring by chance. Nevertheless, over the past few years many such non-canonical genes (with ORFs < 100 AAs) have been discovered in different organisms like Arabidopsis thaliana, Saccharomyces cerevisiae, and Drosophila melanogaster. Thanks to advances in sequencing, bioinformatics and computing power, it is now possible to scan the genome in unprecedented scrutiny, for example in a search of this type of small ORFs.
npj Genomic Medicine
Uncharacterized and unannotated open-reading frames, which we refer to as novel open reading frames (nORFs), may sometimes encode peptides that remain unexplored for novel therapeutic opportunities. To our knowledge, no systematic identification and characterization of transcripts encoding nORFs or their translation products in cancer, or in any other physiological process has been performed. We use our curated nORFs database (nORFs.org), together with RNA-Seq data from The Cancer Genome Atlas (TCGA) and Genotype-Expression (GTEx) consortiums, to identify transcripts containing nORFs that are expressed frequently in cancer or matched normal tissue across 22 cancer types. We show nORFs are subject to extensive dysregulation at the transcript level in cancer tissue and that a small subset of nORFs are associated with overall patient survival, suggesting that nORFs may have prognostic value. We also show that nORF products can form protein-like structures with post-translational modifi...