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Bacterial multidrug efflux transporters (MATEs) couple drug export to Na+ or H+ influx. A new crystal structure of the H+-coupled DinF transporter from Bacillus halodurans reveals differences in the substrate-binding sites and transport mechanisms of DinF and NorM MATE homologs.
Polycomb repressive complex 2 (PRC2) acts as an epigenetic repressor by depositing repressive H3K27me3 marks, but how it is regulated and directed to specific genes remains unknown. PRC2 is now found to bind at low levels to many gene promoters, including active ones devoid of H3K27me3, and the EZH2 catalytic subunit binds directly to nascent transcripts.
A new bacterial toxin from pathogen Photorhabdus asymbiotica is now described. The toxin contains a domain with glycosyltransferase activity that modifies a tyrosine residue of Rho GTPases in the host cell, inhibiting Rho activation and interaction with downstream effectors. The second domain is a glutamine deamidase that blocks GTP hydrolysis by Gaq/11 and Gai proteins.
The dNTPase SAMHD1 inhibits infection by HIV-1 and other retroviruses. In the presence of dGTP, the enzyme forms tetramers and becomes active, a process that is now elucidated by structural, biochemical and cellular analyses of human SAMHD1. Binding of dGTP to four allosteric sites promotes tetramerization and induces a conformational change in the substrate-binding pocket to activate the enzyme.
The Ccr4–Not complex is involved in several aspects of gene expression, including mRNA decay, translational repression and transcription. Structural, biochemical and functional analyses of the Not module, comprising the C-terminal regions of Not1, Not2 and Not5, suggest that it forms a platform for protein and nucleic acid interactions that are important for Ccr4–Not's many functions.
The CCR4–NOT deadenylase complex has a crucial role in post-transcriptional mRNA regulation, catalyzing the removal of mRNA poly(A) tails and consequently repressing translation and promoting mRNA degradation. The crystal structure of the human NOT module, formed by the CNOT1, CNOT2 and CNOT3 C-terminal regions, now provides a structural framework for understanding its assembly and functions.
It has been challenging to label endogenous genomic sequences in living cells, and this has limited attempts to study the dynamics of nuclear architecture in genome function. In a newly developed methodology, transcription activator–like effectors (TALEs) were used to label endogenous repetitive genomic sequences to visualize nuclear positioning and chromatin dynamics in cultured mouse cells and embryos.
Analysis of data from The Cancer Genome Atlas generates a pan-cancer network of 143 recurrent miRNA-target relationships. The identified miRNAs were frequently regulated by genetic and epigenetic alterations in cancer. The work also reveals that some miRNAs might coordinately regulate cancer pathways, such as miR-29 regulation of TET1 and TDG mRNAs, encoding components from the active DNA demethylation pathway.
Mitochondrial DNA is transcribed by a single-subunit RNA polymerase (mtRNAP) that is distantly related to the RNAP of bacteriophage T7. Together with biochemical data, the crystal structure of the mtRNAP elongation complex with DNA template and RNA transcript elucidates the elongation mechanism of mtRNAP and reveals striking differences as compared with the T7 transcription system.
Sodium-coupled glutamate transporters regulate excitatory signaling in the brain. A new crystal structure shows how the substrate induces changes in the binding pocket of an archaeal transporter homolog, providing new insights into the mechanism of transport.
Translation initiation in eukaryotes is a complex and highly regulated process during which several initiation factors cooperate to recruit an initiator tRNA to the small ribosomal subunit, where the mRNA is scanned for an AUG start codon. Two recent reports provide new structural insights into this process and reveal key functions of initiation factors 1 (eIF1) and 1A (eIF1A) in start-codon selection in atomic detail.
