bims-micpro Biomed News
on Discovery and characterization of microproteins
Issue of 2021‒07‒11
three papers selected by
Thomas Martinez
Salk Institute for Biological Studies

  1. DNA Res. 2021 Jul 07. pii: dsab007. [Epub ahead of print]
      Small open reading frames (small ORFs/sORFs/smORFs) are potentially coding sequences smaller than 100 codons that have historically been considered junk DNA by gene prediction software and in annotation screening; however, the advent of next-generation sequencing has contributed to the deeper investigation of junk DNA regions and their transcription products, resulting in the emergence of smORFs as a new focus of interest in systems biology. Several smORF peptides were recently reported in noncanonical mRNAs as new players in numerous biological contexts; however, their relevance is still overlooked in coding potential analysis. Hence, this review proposes a smORF classification based on transcriptional features, discussing the most promising approaches to investigate smORFs based on their different characteristics. First, smORFs were divided into nonexpressed (intergenic) and expressed (genic) smORFs. Second, genic smORFs were classified as smORFs located in noncoding RNAs (ncRNAs) or canonical mRNAs. Finally, smORFs in ncRNAs were further subdivided into sequences located in small or long RNAs, whereas smORFs located in canonical mRNAs were subdivided into several specific classes depending on their localization along the gene. We hope that this review provides new insights into large-scale annotations and reinforces the role of smORFs as essential components of a hidden coding DNA world.
    Keywords:  alternative ORFs; dual functional RNA; genome annotation; long noncoding RNA; smORF peptides
  2. Front Plant Sci. 2021 ;12 695439
      Small peptides (sPeptides), <100 amino acids (aa) long, are encoded by small open reading frames (sORFs) often found in the 5' and 3' untranslated regions (or other parts) of mRNAs, in long non-coding RNAs, or transcripts from introns and intergenic regions; various sPeptides play important roles in multiple biological processes. In this study, we conducted a comprehensive study of maize (Zea mays) sPeptides using mRNA sequencing, ribosome profiling (Ribo-seq), and mass spectrometry (MS) on six tissues (each with at least two replicates). To identify maize sORFs and sPeptides from these data, we set up a robust bioinformatics pipeline and performed a genome-wide scan. This scan uncovered 9,388 sORFs encoding peptides of 2-100 aa. These sORFs showed distinct genomic features, such as different Kozak region sequences, higher specificity of translation, and high translational efficiency, compared with the canonical protein-coding genes. Furthermore, the MS data verified 2,695 sPeptides. These sPeptides perfectly discriminated all the tissues and were highly associated with their parental genes. Interestingly, the parental genes of sPeptides were significantly enriched in multiple functional gene ontology terms related to abiotic stress and development, suggesting the potential roles of sPeptides in the regulation of their parental genes. Overall, this study lays out the guidelines for genome-wide scans of sORFs and sPeptides in plants by integrating Ribo-seq and MS data and provides a more comprehensive resource of functional sPeptides in maize and gives a new perspective on the complex biological systems of plants.
    Keywords:  Ribo-seq; maize; mass spectrometry; small open reading frame; small peptide
  3. Nucleic Acids Res. 2021 Jul 06. pii: gkab549. [Epub ahead of print]
      Although ribosome-profiling and translation initiation sequencing (TI-seq) analyses have identified many noncanonical initiation codons, the precise detection of translation initiation sites (TISs) remains a challenge, mainly because of experimental artifacts of such analyses. Here, we describe a new method, TISCA (TIS detection by translation Complex Analysis), for the accurate identification of TISs. TISCA proved to be more reliable for TIS detection compared with existing tools, and it identified a substantial number of near-cognate codons in Kozak-like sequence contexts. Analysis of proteomics data revealed the presence of methionine at the NH2-terminus of most proteins derived from near-cognate initiation codons. Although eukaryotic initiation factor 2 (eIF2), eIF2A and eIF2D have previously been shown to contribute to translation initiation at near-cognate codons, we found that most noncanonical initiation events are most probably dependent on eIF2, consistent with the initial amino acid being methionine. Comprehensive identification of TISs by TISCA should facilitate characterization of the mechanism of noncanonical initiation.