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Glutamine synthetase (GS) is the key enzyme of nitrogen assimilation induced under nitrogen limiting conditions. The carbon skeleton of glutamate and glutamine, 2-oxoglutarate, is supplied from the TCA cycle, but how this metabolic flow is controlled in response to nitrogen availability remains unknown. We show that the expression of the E1o component of 2-oxoglutarate dehydrogenase, SucA, is repressed under nitrogen limitation in Salmonella enterica and Escherichia coli. The repression is exerted at the post-transcriptional level by an Hfq-dependent sRNA GlnZ generated from the 3′UTR of the GS-encoding glnA mRNA. Enterobacterial GlnZ variants contain a conserved seed sequence and primarily regulate sucA through base-pairing far upstream of the translation initiation region. During growth on glutamine as the nitrogen source, the glnA 3′UTR deletion mutants expressed SucA at higher levels than the S. enterica and E. coli wild-type strains, respectively. In E. coli, the transcriptional regulator Nac also participates in the repression of sucA. Lastly, this study clarifies that the release of GlnZ from the glnA mRNA by RNase E is essential for the post-transcriptional regulation of sucA. Thus, the mRNA coordinates the two independent functions to balance the supply and demand of the fundamental metabolites.

Glutamine synthetase (GS) is the key enzyme of nitrogen assimilation induced under nitrogen limiting conditions. The carbon skeleton of glutamate and glutamine, 2-oxoglutarate, is supplied from the TCA cycle, but how this metabolic flow is controlled in response to nitrogen availability remains unknown. We show that the expression of the E1o component of 2-oxoglutarate dehydrogenase, SucA, is repressed under nitrogen limitation in

The reconstructed in vitro translation system known as the PURE system has been used in a variety of cell-free experiments such as the expression of native and de novo proteins as well as various display methods to select for functional polypeptides. We developed a refined PURE-based display method for the preparation of stable messenger RNA (mRNA) and complementary DNA (cDNA)-peptide conjugates and validated its utility for in vitro selection. Our conjugate formation efficiency exceeded 40%, followed by gel purification to allow minimum carry-over of components from the translation system to the downstream assay enabling clean and efficient random peptide sequence screening. We chose the commercially available anti-FLAG M2 antibody as a target molecule for validation. Starting from approximately 1.7 × 1012 random sequences, a round-by-round high-throughput sequencing showed clear enrichment of the FLAG epitope DYKDDD as well as revealing consensus FLAG epitope motif DYK(D/L/N)(L/Y/D/N/F)D. Enrichment of core FLAG motifs lacking one of the four key residues (DYKxxD) indicates that Tyr (Y) and Lys (K) appear as the two key residues essential for binding. Furthermore, the comparison between mRNA display and cDNA display method resulted in overall similar performance with slightly higher enrichment for mRNA display. We also show that gel purification steps in the refined PURE-based display method improve conjugate formation efficiency and enhance the enrichment rate of FLAG epitope motifs in later rounds of selection especially for mRNA display. Overall, the generalized procedure and consistent performance of two different display methods achieved by the commercially available PURE system will be useful for future studies to explore the sequence and functional space of diverse polypeptides.

Glutamine synthetase is the key enzyme of nitrogen assimilation, which is encoded in the first cistron ofglnALGoperon and is induced under nitrogen limiting conditions through transcriptional activation by NtrBC inSalmonellaandE. coli. 2-oxoglutarate serves as the carbon skeleton of glutamate and glutamine, but how 2-oxoglutarate fluctuation is controlled in response to nitrogen availability remained unknown. We show that theglnAmRNA produces an Hfq-dependent GlnZ sRNA from its 3’ sUTR through RNase E-mediated cleavage. Through a base-pairing mechanism, GlnZ primarily regulatessucA, encoding the E1o component of 2-oxoglutarate dehydrogenase. In the cells grown on glutamine as the nitrogen source, the endogenous GlnZ represses the expression of SucA to redirect the carbon flow from the TCA cycle to the nitrogen assimilation pathway. This study also clarifies that the release of GlnZ sRNA from theglnAmRNA by RNase E is essential for the post-transcriptional regulation ofsucA, and thus the mRNA coordinates the two independent functions to balance the supply and demand of the fundamental metabolites.

International audience; Splicing factor mutations are frequent in myeloid neoplasms, blood cancers,and solid tumors. Cancer cells harboring these mutations present aparticular vulnerability to drugs that target splicing factors such asSF3b155 or CAPERα. Still, the arsenal of chemical probes that targets thespliceosome is very limited. U2AF homology motifs (UHMs) are commonprotein interaction domains among splicing factors. They present ahydrophobic pocket ideally suited to anchor small molecules with the aimto inhibit protein–protein interaction. Here, we combined a virtual screeningof a small molecules database and an in vitro competition assay andidentified a small molecule, we named UHMCP1 that prevents theSF3b155/U2AF interaction. NMR analyses and molecular dynamics simulationsconfirmed the binding of this molecule in the hydrophobic pocketof the U2AF UHM domain. We further provide evidence that UHMCP1impacts splicing and cell viability and is therefore an interesting novel compoundtargeting an UHM domain with potential anticancer properties.

The recombinant in vitro translation system known as the PURE system has been used in a variety of cell-free experiments such as expression of native and de novo proteins as well as various display methods to select for functional polypeptides. We developed a refined PURE-based display method for the preparation of stable mRNA and cDNA-peptide conjugates and validated its utility for in vitro selection. Our conjugate formation efficiency exceeded 40%, followed by gel purification to allow minimum carry-over of components from the translation system to the downstream assay enabling clean and efficient random peptide sequence screening. As a proof-of-concept, we chose the commercially available anti-FLAG M2 antibody as a target molecule for validation. Starting from approximately 1.7 x 1012 random sequences, a round-by-round high-throughput sequencing showed clear enrichment of the FLAG epitope DYKDDD as well as revealing consensus FLAG binding motif DYK(D/L/N)(L/Y/D/N/F)D. Enrichment of core FLAG motifs lacking one of the four key residues (DYKxxD) indicates that Tyr (Y) and Lys (K) appear as the two key residues essential for binding. Furthermore, comparison between mRNA display and cDNA display method resulted in overall similar performance with slightly higher enrichment for mRNA display. The consistency of two different display methods achieved by commercially available PURE system will be useful for future studies to explore sequence and functional space of diverse polypeptides.

International audience; The essential splicing factor U2AF65 is known to help anchoring U2 snRNP at the branch site. Its C-terminal UHM domain interacts with ULM motifs of SF3b155, an U2 snRNP protein. Here, we report a cooperative binding of U2AF65 and the related protein CAPERα to the multi-ULM domain of SF3b155. In addition, we show that the RS domain of U2AF65 drives a liquid-liquid phase separation that is amplified by intronic RNA with repeated pyrimidine tracts. In cells, knockdown of either U2AF65 or CAPERα improves the inclusion of cassette exons that are preceded by such repeated pyrimidine-rich motifs. These results support a model in which liquid-like assemblies of U2AF65 and CAPERα on repetitive pyrimidine-rich RNA sequences are driven by their RS domains, and facilitate the recruitment of the multi-ULM domain of SF3b155. We anticipate that posttranslational modifications and proteins recruited in dynamical U2AF65 and CAPERα condensates may further contribute to the complex mechanisms leading to specific splice site choice that occurs in cells.

The essential splicing factor U2AF (65) is known to help anchoring U2 snRNP at the branch site. Its C‐terminal UHM domain interacts with ULM motifs of SF3b155, an U2 snRNP protein. Here, we report a cooperative binding of U2AF (65) and the related protein CAPERα to the multi‐ULM domain of SF3b155. In addition, we show that the RS domain of U2AF (65) drives a liquid–liquid phase separation that is amplified by intronic RNA with repeated pyrimidine tracts. In cells, knockdown of either U2AF (65) or CAPERα improves the inclusion of cassette exons that are preceded by such repeated pyrimidine‐rich motifs. These results support a model in which liquid‐like assemblies of U2AF (65) and CAPERα on repetitive pyrimidine‐rich RNA sequences are driven by their RS domains, and facilitate the recruitment of the multi‐ULM domain of SF3b155. We anticipate that posttranslational modifications and proteins recruited in dynamical U2AF (65) and CAPERα condensates may further contribute to the complex mechanisms leading to specific splice site choice that occurs in cells.

International audience; Prokaryotes encounter constant and often brutal modifications to their environment. In order to survive, they need to maintain fitness, which includes adapting their protein expression patterns. Many factors control gene expression but this review focuses on just one, namely antisense RNAs (asRNAs), a class of non-coding RNAs (ncRNAs) characterized by their location in cis and their perfect complementarity with their targets. asRNAs were considered for a long time to be trivial and only to be found on mobile genetic elements. However, recent advances in methodology have revealed that their abundance and potential activities have been underestimated. This review aims to illustrate the role of asRNA in various physiologically crucial functions in both archaea and bacteria, which can be regrouped in three categories: cell maintenance, horizontal gene transfer and virulence. A literature survey of asRNAs demonstrates the difficulties to characterize and assign a role to asRNAs. With the aim of facilitating this task, we describe recent technological advances that could be of interest to identify new asRNAs and to discover their function.