A genome-wide survey of short coding sequences in

Unité de Biochimie Bactérienne, UR477, INRA, 78350 Jouy-en-Josas, France.
Microbiology (Impact Factor: 2.56). 12/2007; 153(Pt 11):3631-44. DOI: 10.1099/mic.0.2007/006205-0
Source: PubMed


Identification of short genes that encode peptides of fewer than 60 aa is challenging, both experimentally and in silico. As a consequence, the universe of these short coding sequences (CDSs) remains largely unknown, although some are acknowledged to play important roles in cell-cell communication, particularly in Gram-positive bacteria. This paper reports a thorough search for short CDSs across streptococcal genomes. Our bioinformatic approach relied on a combination of advanced intrinsic and extrinsic methods. In the first step, intrinsic sequence information (nucleotide composition and presence of RBSs) served to identify new short putative CDSs (spCDSs) and to eliminate the differences between annotation policies. In the second step, pseudogene fragments and false predictions were filtered out. The last step consisted of screening the remaining spCDSs for lines of extrinsic evidence involving sequence and gene-context comparisons. A total of 789 spCDSs across 20 complete genomes (19 Streptococcus and one Enterococcus) received the support of at least one line of extrinsic evidence, which corresponds to an average of 20 short CDSs per million base pairs. Most of these had no known function, and a significant fraction (31%) are not even annotated as hypothetical genes in GenBank records. As an illustration of the value of this list, we describe a new family of CDSs, encoding very short hydrophobic peptides (20-23 aa) situated just upstream of some of the positive transcriptional regulators of the Rgg family. The expression of seven other short CDSs from Streptococcus thermophilus CNRZ1066 that encode peptides ranging in length from 41 to 56 aa was confirmed by real-time quantitative RT-PCR and revealed a variety of expression patterns. Finally, one peptide from this list, encoded by a gene that is not annotated in GenBank, was identified in a cell-envelope-enriched fraction of S. thermophilus CNRZ1066.

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Available from: Véronique Monnet, May 04, 2015
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    • "After the discovery that the deletion of a small pre-peptide gene inhibited the regulatory activity of an Rgg protein in S. thermophilus, it was recognized that activity of Rgg regulators was modulated by short peptides, constituting putative QS circuits (Ibrahim et al., 2007a). Commonly, Rgg genes are located next to a short open reading frame that encodes the propeptide of their cognate pheromone, short genes which are usually overlooked in genome annotation processes but have been predicted by in silico analysis (Ibrahim et al., 2007b; Fleuchot et al., 2011). Rgg pheromones have been classified in two groups to date, short hydrophobic peptides (SHPs) and peptides involved in competence pathways, termed XIPs (Table 1) (Mashburn-Warren et al., 2010; Fleuchot et al., 2011). "
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    • "Most of them characterized up to now, are encoded by short open reading frames (ORFs), which have been only heterogeneously and incompletely annotated in genome sequences. In a survey of 20 streptococcal genomes, purpose-built detection software predicted the putative occurrence of 20 short ORFs per million bp; of these, nearly onethird lacked any form of annotation (Ibrahim et al., 2007a). Figure 1. "
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    • ": 1) Known RNA genes identified individually by 5′ end mapping and Northern blot analysis, reported in the literature. 2) New RNA genes, so called independent transcription units identified through the large scale tiling array analysis described in [31]; 3) New CDSs, unannotated expressed regions described in [31] and containing a coding sequence detected with high confidence by SHOW, based on an enriched HMM model of DNA sequences [45]; 4) 5′ cis-acting structures compiled from [30], and reliable predictions against the RFAM database [46], reported in the Genome Reviews version of annotated genomes from the EBI [47]; 5) Newly expressed antisense segments, complementary to expressed regions corresponding to 5′ UTRs, 3′ UTRs, and intergenic regions of annotated features; 6) Newly expressed segments not antisense, classified as in the previous item, but not antisense, see [31] for criteria distinguishing antisense regions from those that are not. We refer to all RNAs described here using the same «segment» (S) number and classification as in [31] which corresponds to their order of appearance on the B. subtilis genome. "
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