RESUMEN
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 defining translation of these novel smORFs in lncRNAs and UTRs. We also look at some of the bioinformatic and biochemical approaches used to independently corroborate these exciting new findings and elucidate real translation events.
Asunto(s)
Secuenciación de Nucleótidos de Alto Rendimiento/métodos , Sistemas de Lectura Abierta/genética , Biosíntesis de Proteínas/genética , Proteoma/genética , Ribosomas/genética , Regiones no Traducidas 3'/genética , Biología Computacional/métodos , Modelos Genéticos , Polirribosomas/genética , Polirribosomas/metabolismo , Proteoma/metabolismo , ARN Largo no Codificante/genética , Ribosomas/metabolismoRESUMEN
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.