A role for REP sequences in regulating translation.

Repetitive extragenic palindromic (REP) sequences are highly structured elements found downstream of ∼500 genes in Escherichia coli that result in extensive stem-loop structures in their mRNAs. However, their physiological role has remained elusive. Here, we show that REP sequences can downregulate translation, but only if they are within 15 nt of a termination codon; a spacing of 16 nt has no effect, suggesting that the REP element acts to stall ribosome movement. Ribosome stalling leads to cleavage of the mRNA and induction of the trans-translation process. Using nrdAB as a model, we find that its regulation can be partially reversed by overexpression of RNA helicases and can be fully overcome upon UV stress, emphasizing the importance of this regulatory process. Since 50% of REP-associated genes have these elements within the critical 15 nt, these findings identify a regulatory mechanism with the potential to affect translation from a large number of genes.

GenoBase: comprehensive resource database of Escherichia coli K-12.

Comprehensive experimental resources, such as ORFeome clone libraries and deletion mutant collections, are fundamental tools for elucidation of gene function. Data sets by omics analysis using these resources provide key information for functional analysis, modeling and simulation both in individual and systematic approaches. With the long-term goal of complete understanding of a cell, we have over the past decade created a variety of clone and mutant sets for functional genomics studies of Escherichia coli K-12. We have made these experimental resources freely available to the academic community worldwide. Accordingly, these resources have now been used in numerous investigations of a multitude of cell processes. Quality control is extremely important for evaluating results generated by these resources. Because the annotation has been changed since 2005, which we originally used for the construction, we have updated these genomic resources accordingly. Here, we describe GenoBase (http://ecoli.naist.jp/GB/), which contains key information about comprehensive experimental resources of E. coli K-12, their quality control and several omics data sets generated using these resources.

Structural analysis and mutant growth properties reveal distinctive enzymatic and cellular roles for the three major L-alanine transaminases of Escherichia coli.

In order to maintain proper cellular function, the metabolism of the bacterial microbiota presents several mechanisms oriented to keep a correctly balanced amino acid pool. Central components of these mechanisms are enzymes with alanine transaminase activity, pyridoxal 5'-phosphate-dependent enzymes that interconvert alanine and pyruvate, thereby allowing the precise control of alanine and glutamate concentrations, two of the most abundant amino acids in the cellular amino acid pool. Here we report the 2.11-Å crystal structure of full-length AlaA from the model organism Escherichia coli, a major bacterial alanine aminotransferase, and compare its overall structure and active site composition with detailed atomic models of two other bacterial enzymes capable of catalyzing this reaction in vivo, AlaC and valine-pyruvate aminotransferase (AvtA). Apart from a narrow entry channel to the active site, a feature of this new crystal structure is the role of an active site loop that closes in upon binding of substrate-mimicking molecules, and which has only been previously reported in a plant enzyme. Comparison of the available structures indicates that beyond superficial differences, alanine aminotransferases of diverse phylogenetic origins share a universal reaction mechanism that depends on an array of highly conserved amino acid residues and is similarly regulated by various unrelated motifs. Despite this unifying mechanism and regulation, growth competition experiments demonstrate that AlaA, AlaC and AvtA are not freely exchangeable in vivo, suggesting that their functional repertoire is not completely redundant thus providing an explanation for their independent evolutionary conservation.

EcoGene-RefSeq: EcoGene tools applied to the RefSeq prokaryotic genomes.

SUMMARY: EcoGene.org is a genome database and website dedicated to Escherichia coli K-12 substrain MG1655 that is revised daily using information derived from the biomedical literature and in-house analysis. EcoGene is a major source of annotation updates for the MG1655 Genbank record, one of only a few Genbank genome records that are updated by a community effort. The Reference Sequence (RefSeq) database, built by The National Center for Biotechnology Information, comprises a set of duplicate Genbank genome records that can be modified by the NCBI staff annotators. EcoGene-RefSeq is being developed as a stand-alone internet resource to facilitate the usage of EcoGene-based tools on any of the >2400 completed prokaryotic genome records that are currently available at the RefSeq database. AVAILABILITY: The web interface of EcoGene-RefSeq is available at http://www.ecogene.org/refseq. CONTACT: krudd@med.miami.edu or j.zhou1@miami.edu.

EcoGene 3.0.

EcoGene (http://ecogene.org) is a database and website devoted to continuously improving the structural and functional annotation of Escherichia coli K-12, one of the most well understood model organisms, represented by the MG1655(Seq) genome sequence and annotations. Major improvements to EcoGene in the past decade include (i) graphic presentations of genome map features; (ii) ability to design Boolean queries and Venn diagrams from EcoArray, EcoTopics or user-provided GeneSets; (iii) the genome-wide clone and deletion primer design tool, PrimerPairs; (iv) sequence searches using a customized EcoBLAST; (v) a Cross Reference table of synonymous gene and protein identifiers; (vi) proteome-wide indexing with GO terms; (vii) EcoTools access to >2000 complete bacterial genomes in EcoGene-RefSeq; (viii) establishment of a MySql relational database; and (ix) use of web content management systems. The biomedical literature is surveyed daily to provide citation and gene function updates. As of September 2012, the review of 37 397 abstracts and articles led to creation of 98 425 PubMed-Gene links and 5415 PubMed-Topic links. Annotation updates to Genbank U00096 are transmitted from EcoGene to NCBI. Experimental verifications include confirmation of a CTG start codon, pseudogene restoration and quality assurance of the Keio strain collection.

YhiQ is RsmJ, the methyltransferase responsible for methylation of G1516 in 16S rRNA of E. coli.

Ten methyltransferases and one pseudouridine synthase are required for complete modification of the small ribosomal subunit in Escherichia coli. Nine methyltransferases, as well as the pseudouridine synthase, are already known. Here, we identify RsmJ, the last unknown methyltransferase required for methylation of m(2)G1516 in 16S ribosomal RNA (rRNA), as the protein encoded by yhiQ. Reverse transcription primer extension analysis reveals that rRNA extracted from a yhiQ deletion strain is not methylated at G1516. Moreover, methylation is restored upon gene complementation. Also, purified recombinant YhiQ specifically methylates 30S subunits extracted from the deletion strain. The absence of the yhiQ gene leads to a cold-sensitive phenotype. Based on these data, we propose that the yhiQ gene be renamed rsmJ.

Bacterial genome reengineering.

The web application PrimerPair at ecogene.org generates large sets of paired DNA sequences surrounding- all protein and RNA genes of Escherichia coli K-12. Many DNA fragments, which these primers amplify, can be used to implement a genome reengineering strategy using complementary in vitro cloning and in vivo recombineering. The integration of a primer design tool with a model organism database increases the level of quality control. Computer-assisted design of gene primer pairs relies upon having highly accurate genomic DNA sequence information that exactly matches the DNA of the cells being used in the laboratory to ensure predictable DNA hybridizations. It is equally crucial to have confidence that the predicted start codons define the locations of genes accurately. Annotations in the EcoGene database are queried by PrimerPair to eliminate pseudogenes, IS elements, and other problematic genes before the design process starts. These projects progressively familiarize users with the EcoGene content, scope, and application interfaces that are useful for genome reengineering projects. The first protocol leads to the design of a pair of primer sequences that were used to clone and express a single gene. The N-terminal protein sequence was experimentally verified and the protein was detected in the periplasm. This is followed by instructions to design PCR primer pairs for cloning gene fragments encoding 50 periplasmic proteins without their signal peptides. The design process begins with the user simply designating one pair of forward and reverse primer endpoint positions relative to all start and stop codon positions. The gene name, genomic coordinates, and primer DNA sequences are reported to the user. When making chromosomal deletions, the integrity of the provisional primer design is checked to see whether it will generate any unwanted double deletions with adjacent genes. The bad designs are recalculated and replacement primers are provided alongside the requested primers. A list of all genes with overlaps includes those expressed from the translational coupling motifs 5'-UGAUG-3' and 5'-AUGA-3'. Rigid alignments of the 893 ribosome binding sites (RBSs) linked to the AUG codons of this coupled subset are assessed for information content using WebLogo 3.0. These specialized logos are missing the G at the prominent information peak position normally seen in the rigid alignment of all genes. This novel GHOLE motif was apparently masked by the normal RBSs in two previously published rigid alignments. We propose a model constraining the distance between the ATG and the RBS, obviating- the need for a flexible linker model to reveal a Shine-Dalgarno-like sequence.

Repression of small toxic protein synthesis by the Sib and OhsC small RNAs.

The sequences encoding the QUAD1 RNAs were initially identified as four repeats in Escherichia coli. These repeats, herein renamed SIB, are conserved in closely related bacteria, although the number of repeats varies. All five Sib RNAs in E. coli MG1655 are expressed, and no phenotype was observed for a five-sib deletion strain. However, a phenotype reminiscent of plasmid addiction was observed for overexpression of the Sib RNAs, and further examination of the SIB repeat sequences revealed conserved open reading frames encoding highly hydrophobic 18- to 19-amino-acid proteins (Ibs) opposite each sib gene. The Ibs proteins were found to be toxic when overexpressed and this toxicity could be prevented by coexpression of the corresponding Sib RNA. Two other RNAs encoded divergently in the yfhL-acpS intergenic region were similarly found to encode a small hydrophobic protein (ShoB) and an antisense RNA regulator (OhsC). Overexpression of both IbsC and ShoB led to immediate changes in membrane potential suggesting both proteins affect the cell envelope. Whole genome expression analysis showed that overexpression of IbsC and ShoB, as well as the small hydrophobic LdrD and TisB proteins, has both overlapping and unique consequences for the cell.

Small membrane proteins found by comparative genomics and ribosome binding site models.

The correct annotation of genes encoding the smallest proteins is one of the biggest challenges of genome annotation, and perhaps more importantly, few annotated short open reading frames have been confirmed to correspond to synthesized proteins. We used sequence conservation and ribosome binding site models to predict genes encoding small proteins, defined as having 16-50 amino acids, in the intergenic regions of the Escherichia coli genome. We tested expression of these predicted as well as previously annotated genes by integrating the sequential peptide affinity tag directly upstream of the stop codon on the chromosome and assaying for synthesis using immunoblot assays. This approach confirmed that 20 previously annotated and 18 newly discovered proteins of 16-50 amino acids are synthesized. We summarize the properties of these small proteins; remarkably more than half of the proteins are predicted to be single-transmembrane proteins, nine of which we show co-fractionate with cell membranes.

Escherichia coli K-12: a cooperatively developed annotation snapshot--2005.

The goal of this group project has been to coordinate and bring up-to-date information on all genes of Escherichia coli K-12. Annotation of the genome of an organism entails identification of genes, the boundaries of genes in terms of precise start and end sites, and description of the gene products. Known and predicted functions were assigned to each gene product on the basis of experimental evidence or sequence analysis. Since both kinds of evidence are constantly expanding, no annotation is complete at any moment in time. This is a snapshot analysis based on the most recent genome sequences of two E.coli K-12 bacteria. An accurate and up-to-date description of E.coli K-12 genes is of particular importance to the scientific community because experimentally determined properties of its gene products provide fundamental information for annotation of innumerable genes of other organisms. Availability of the complete genome sequence of two K-12 strains allows comparison of their genotypes and mutant status of alleles.

Identification and characterization of RsmE, the founding member of a new RNA base methyltransferase family.

A variety of RNA methyltransferases act during ribosomal RNA maturation to modify nucleotides in a site-specific manner. However, of the 10 base-methylated nucleotides present in the small ribosomal subunit of Escherichia coli, only three enzymes responsible for modification of four bases are known. Here, we show that the protein encoded by yggJ, a member of the uncharacterized DUF558 protein family of predicted alpha/beta (trefoil) knot methyltransferases is responsible for methylation at U1498 in 16S rRNA. The gene is well-conserved across bacteria and plants, and likely performs the same function in other organisms. A yggJ deletion strain lacks the methyl group at U1498 as well as the specific methyltransferase activity. Moreover, purified recombinant YggJ specifically methylates m3U1498 in vitro. The deletion strain was unaffected in exponential growth in rich or minimal media at multiple temperatures, but it was defective when grown in competition with isogenic wild-type cells. Based on these data, we conclude that yggJ is the founding member of a family of RNA base methyltransferases, and propose that it be renamed rsmE.

Fine-tuning the prediction of sequences cleaved by signal peptidase II: a curated set of proven and predicted lipoproteins of Escherichia coli K-12.

A curated set of 81 proven and 44 predicted lipoproteins of Escherichia coli K-12 was defined with the combined use of a literature survey, a variety of predictive tools and human expertise. The well-documented Gram-negative proteome of E. coli K-12 was chosen to assess how the different approaches complement each other and to ensure a stable definition of a consistent set of lipoproteins. The results of detailed analysis of such proteins at the level of a single proteome are presented, corroborated and rationalized.

The second aconitase (AcnB) of Escherichia coli.

The second aconitase (AcnB) of Escherichia coli was partially purified from an acnA::kanR mutant lacking AcnA, and the corresponding polypeptide identified by activity staining and weak cross-reactivity with AcnA antiserum. The acnB gene was located at 2 center dot 85 min (131 center dot 6 kb) in a region of the chromosome previously assigned to two unidentified ORFs. Aconitase specific activities were amplified up to fivefold by infection with lambdaacnB phages from the Kohara lambda-E. coli gene library, and up to 120-fold (50% of soluble protein) by inducing transformants containing a plasmid (pGS783) in which the acnB coding region is expressed from a regulated T7 promoter. The AcnB protein was purified to > or = 98% homogeneity from a genetically enriched source (JRG3171) and shown to be a monomeric protein of Mr 100 000 (SDS-PAGE) and 105 000 (gel filtration analysis) compared with Mr 93 500 predicted from the nucleotide sequence. The sequence identity between AcnA and AcnB is only 17% and the domain organization of AcnA and related proteins (1-2-3-linker-4) is rearranged in AcnB (4-1-2-3).