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Selectivity mechanism of a bacterial homolog of the human drug-peptide transporters PepT1 and PepT2 Guettou et al. describe structural studies on a bacterial homolog of PepT1 and PepT2 peptide transporters—nutrient transporters responsible for all peptide transport across the plasma membrane—in complex with three di- or tripeptides. The data suggest how the transporter's broad peptide specificity is achieved. Structure of the mammalian 80S initiation complex with initiation factor 5B on HCV-IRES RNA Eukaryotic initiation factor 5b (eIF5B) is essential for translation initiation. Spahn and colleagues now report cryo-EM structures of the mammalian 80S initiation complex associated with eIF5B that redefine eIF5B as a tRNA reorientation factor. Identification of genes in toxicity pathways of trinucleotide-repeat RNA in C. elegans A screen identifies 15 genes that modulate CUG-repeat toxicity in C. elegans, including those encoding RNA-export and clearance factors. Toxic RNAs are recognized by the NMD pathway via their 3' UTR GC content. Allosteric enhancement of MAP kinase p38α's activity and substrate selectivity by docking interactions MAP kinases recognize pathway-specific substrates via docking interactions. NMR analyses now reveal that docking interactions also stimulate ATP binding and phosphotransfer activity of p38α via an allosteric mechanism. Structural basis for activity of highly efficient RNA mimics of green fluorescent protein Structural elucidation of the RNA aptamer 'Spinach' reveals that a new G-quadruplex structure forms the fluorophore-binding site that confers the ability of the RNA to function as a GFP mimic. Structural basis for RNA recognition in roquin-mediated post-transcriptional gene regulation Roquin controls T-cell activity through interactions with mRNAs of stimulatory receptors. Structural and functional elucidation of its RNA-binding domain reveals how it interacts with constitutive decay elements in the 3' UTR of its targets to regulate their expression. The ROQ domain of Roquin recognizes mRNA constitutive-decay element and double-stranded RNA Roquin recognizes the CDE element in mRNAs to promote their decay. Crystal structures of human Roquin ROQ domain in complex with RNA reveals two distinct RNA-binding sites for stem-loop RNA and dsRNA. Mechanism of asymmetric polymerase assembly at the eukaryotic replication fork Eukaryotic DNA replication is carried out by two DNA polymerases, Polɛ and Pol δ. An in vitro–replication system reconstituted with purified yeast components identifies the factors that selectively recruit each polymerase for leading- or lagging-strand synthesis. RPRD1A and RPRD1B are human RNA polymerase II C-terminal domain scaffolds for Ser5 dephosphorylation Mammalian RPRD proteins bind the phosphorylated CTD of RNA pol II with different affinities. Structural elucidation and characterization of their CTD interaction domains reveal the basis of RPRD binding preferences and a role in directing CTD dephosphorylation. Molecular basis for unidirectional scaffold switching of human Plk4 in centriole biogenesis Plk4 regulates centriole duplication. Two centrosomal scaffold proteins, Cep192 and Cep152, are shown to interact with Plk4 in a temporally and spatially regulated manner, and structural analyses reveal that these interactions are mutually exclusive. A protein-RNA specificity code enables targeted activation of an endogenous human transcript A randomized RNA library is used to determine the specificities of RNA recognition by PUF repeats. The code is then used to design a protein that targets endogenous human cyclin B1 mRNA and activates its translation. Delivering nonidentical twins Two sibling DNA polymerases synthesize most of the eukaryotic nuclear genome. A new study provides insights into the distinct protein interactions that deliver these replicases for asymmetric leading- and lagging-strand replication and reveals possible cross-talk between DNA replication and other cellular processes.

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