Volume 22 Issue 9, September 2015

Totipotency, the ability of early embryonic cells to generate a complete adult organism as well as extraembryonic tissue, is a fleeting property found only in very early embryonic cells. A breakthrough study now shows that inhibition of DNA replication–linked nucleosome assembly causes embryonic stem cells to resemble totipotent cells. Notably, inhibition of chromatin assembly stimulates reprogramming during somatic-cell nuclear transfer experiments.

Plants protect themselves from fluctuating high-light conditions by dissipating a large part of their absorbed energy as heat, in a process that requires the protein PsbS. The structure of PsbS opens new possibilities for understanding the mechanism of photoprotection in plants.

The eukaryotic 26S proteasome is responsible for degrading virtually any protein with an appropriate ubiquitin signal, and in the process ubiquitin is spared and recycled. Two studies of the proteasome-associated deubiquitinase UBP6 now shed light on how deubiquitination coordinates the cycle of substrate processing.

Two studies using chromosome conformation capture (3C) analyses in the Gram-positive bacterium Bacillus subtilis have revealed a global pattern of chromosome organization that originates from loading sites of the Smc–ScpAB complex. Loading Smc–ScpAB at a single genomic location is sufficient to promote genome-wide folding of DNA into a well-defined structure.

New methods permit genomic mapping of oxidized methylcytosines at single-base resolution and suggest new regulatory functions for 5-methylcytocine (5mC) derivatives 5hmC, 5fC and 5caC in the mammalian genome.

New data show that depletion of histone chaperone CAF-1 in mouse embryonic stem (ES) cells induces early embryonic-like cells that exhibit gene-expression patterns and reprogramming efficiencies characteristic of 2-cell-stage populations that arise spontaneously in ES-cell culture, thus suggesting that altered chromatin assembly contributes to differences in stem-cell plasticity.

The Mycobacterium tuberculosis necrotizing toxin (TNT) is shown to cause toxicity by hydrolyzing NAD⁺ in the host cell. The crystal structure of TNT bound to its immunity factor reveals a new NAD⁺ glycohydrolase fold.

The cocrystal structure of bacterial alarmone ZMP with its cognate riboswitch reveals how the two subdomains of the latter mediate ligand recognition. Supporting biochemical analyses show that ligand binding affinity and transcription antitermination are modulated by the interdomain linker length.

Extensive mutant cycle analysis provides a map of the residues that contribute to stability and activation-associated conformational dynamics of the Gα_i1 protein in nucleotide-bound states and in complex with the G protein–coupled receptor rhodopsin.

Dual effector binding to the small GTPase Rab11 suggests that membrane-targeting complexes involved in vesicular transport might assemble through multiple weak interactions to create high-avidity assemblies.

Mig6 phosphorylation at two consecutive tyrosines induces rearrangements that lead to Mig6 sticking to and inhibiting the same EGFR that catalyzed its phosphorylation. This mechanism may serve as a basis for inhibition of oncogenic EGFR variants.

Electron microscopy and biochemistry analyses reveal that the deubiquitinase Ubp6, in its ubiquitin-bound form, inhibits substrate deubiquitination by Rpn11, stabilizes the proteasome in a substrate-engaged conformation and interferes with the engagement of a subsequent substrate.

Biochemical and structural analyses show that Rubisco accumulation factor 1 (Raf1) stabilizes RbcL dimers, which then assemble into octamers. Raf1 is then displaced by RbcS, thus yielding the Rubisco holoenzyme.

PsbS is a transmembrane photosystem II protein essential for photoprotection in plants. Crystal structures show that PsbS is not a canonical pigment-binding protein and provide insights into its pH-dependent activation mechanism.

The ATM kinase is shown to be recruited to sites of DNA damage, where it phosphorylates H2AX and triggers the G2-M checkpoint, in the absence of both MRN and Ku70–Ku80.

O-GlcNAcylation is a post-translational modification catalyzed by O-GlcNAc transferase. Here, a high-throughput activity assay combined with mass spectrometric and crystallographic analyses sheds light on the substrate recognition and specificity of O-GlcNAc transferase.