Brief Communications

STING is an ER-resident membrane protein that triggers cytokine production upon detection of the bacterial second messenger c-di-GMP. The structures of the cytosolic domain of STING and the complex it forms with c-di-GMP lay the groundwork for understanding STING function.

The process of pre-mRNA splicing involves connecting two exons while releasing the intron as a transient branched RNA, or as a lariat. Deep-sequencing analysis has enabled the first large-scale identification of branch points in human pre-mRNA transcripts in vivo, onto which the distribution of splicing factor binding was mapped.

AMP-activated protein kinase (AMPK) has a central role in sensing cellular metabolic levels. Crystal structures of the AMPK core in the presence of AMP or ATP suggest that the third nucleotide-binding site in the γ subunit is important for allosteric regulation of kinase activity.

Poly ADP-ribosylation regulates cellular processes such as genomic stability maintenance, transcription and cell death. The structure of a mammalian poly(ADP-ribose) glycohydrolase gives insight into the enzyme's endoglycosidase activity and provides a basis for the development of therapeutic inhibitors.

Primary microRNA cleavage by the Microprocessor complex comprising Drosha and DGCR8 needs to be specific yet efficient. Mathematical modeling complemented with experimental analysis now shows that autoregulatory feedback on DGCR8 expression is crucial for balancing the efficiency and specificity of Microprocessor activity.

Group II introns, which are self-splicing catalytic RNAs, catalyze splicing in two distinct steps. The crystal structure of a group II intron in the pre-catalytic state directly preceding the first splicing step reveals a sharp kink in the backbone that presents the scissile phosphate of the splice site to the active site.

Interleukin-1 (IL-1) cytokines are important mediators of the innate and adaptive immune response. The structure of IL-1β bound to its receptor (IL-IR) and receptor accessory protein (IL-1RAcP) provides an important model for how these cytokines initiate signaling.

SUMOylation targets HP1α to pericentric heterochromatin, but the enzyme responsible for removing the SUMO molecule from HP1α has not been determined. SENP7 is now identified as the factor that deconjugates SUMO, promoting retention of HP1α at these domains.

The crystal structure of the fusion protein from human metapneumovirus in complex with a potently neutralizing antibody reveals a novel antigenic site, which could be explored to develop vaccines against this and related paramyxoviruses.

Numerous methylated residues exist on histone tails, the functional significance of which remains unknown. New studies in budding yeast now identify monomethylation of histone H4 lysine residues 5, 8 and 12 as functionally important marks that regulate cell growth and stress responses and are catalyzed by the first known H4 methyltransferase in budding yeast, Set5.

Some bacterial pathogens can obtain iron from the human host by extracting it from transferrin via two bacterial surface proteins, TfbA and TfbB. Now the crystal structures of Neisseria meningitidis TfbB in its apo state and bound to human transferrin reveal how TfbB sequesters transferrin and initiates iron release.

Glutamate transporters couple the uptake of glutamate to the transport of cations. A new crystal structure of an archaeal trimeric glutamate transporter homolog, GltPh, captured in an intermediate conformation between the outward and inward facing states, provides insights into the transport mechanism.

Nuclear chromodomain-containing proteins read the epigenetic code by recognizing methylated lysine residues in histone tails. Structural analysis of the cytoplasmic chloroplast signal recognition particle subunit cpSRP34 in complex with the cpSRP54 subunit C-terminal tail comprising an arginine-rich motif reveals that a twinned aromatic cage reads two neighboring nonmethylated arginine residues and adapts chromodomains to a function outside the nucleus.

Recent work has indicated that the Escherichia coli replisome contains three DNA polymerases that are used to replicate two parental strands. A single-molecule approach is now used to compare replisomes reconstituted with two or three polymerases, revealing that the presence of a third polymerase ensures higher processivity overall and more efficient replication of the lagging strand.

The surface glycoprotein of the distinct ebolavirus responsible for the largest outbreak yet described (Sudan Gulu) has been crystallized in complex with a novel, neutralizing antibody. The crystal structure and accompanying in vitro and in vivo experiments demonstrate that the antibody functions after virus entry and illustrates a key hotspot for ebolavirus neutralization.

The Fanconi anemia (FA) DNA-repair pathway is important in processing of DNA interstrand cross-links and in resistance to exogenously added aldehyde. Genetic analyses now reveal the synthetic lethality of deficiencies in the FA pathway and formaldehyde catabolism, indicting that this pathway repairs lesions caused by endogenous formaldehyde.

The FET family proteins FUS, EWSR1 and TAF15 are RNA-binding proteins with diverse nuclear functions. PAR-CLIP analyses now reveal the genome-wide RNA targets of all three human FET proteins and of two FUS mutants that cause amyotrophic lateral sclerosis. Although the RNA-binding properties of the mutants remain unchanged, the spectrum of RNA targets is altered because of the changed subcellular localization of the mutants.

Common fragile sites (CFSs) can drive genomic instability. The basis for their fragile nature is not clear, but lymphocyte CFSs have been mapped to regions with low replication initiation events and late replication completion. These features are now used to rapidly identify CFSs in different fibroblast cells.

During protein synthesis, mRNA and tRNAs are iteratively translocated by the ribosome, but which molecular event is rate limiting for translocation has been unknown. Kinetics analyses now reveal that disruption of the interactions between the A-site codon and the ribosome accelerates translocation, suggesting that mRNA release from the decoding center of the ribosome is the rate-limiting step.

Aprataxin is a DNA deadenylase that processes DNA molecules with 5'-AMP termini that result from abortive ligation reactions. The crystal structures of the Schizosaccharomyces pombe ortholog Hnt3 in its apo state, bound to DNA or DNA and AMP, provide insight into how this enzyme recognizes and processes its substrate.