Reviews & Analysis

In vitro reconstitution of recognition of 80S ribosomes by CCR4–NOT, cryo-electron microscopy (cryoEM), crosslinking mass spectrometry and biochemical characterization reveal that CCR4–NOT specifically identifies ribosomes stalled during translation elongation. CCR4–NOT occupies the ribosomal exit site (E site) and locks the ribosomal L1 stalk in an open conformation to enforce the stalled state.

New work shows that in mammals, the iDDR motif of telomere factor TRF2 inhibits the MRE11–RAD50–NBS1 (MRN) complex at chromosome ends through a direct iDDR–RAD50 interaction. Unrelated protein motifs in yeasts inhibit MRN functions via an analogous mechanism, suggesting a convergent evolution in eukaryotes to control MRN action at telomeres.

Here we report Droplet Paired-Tag, a rapid and robust method to simultaneously profile histone modifications and gene expression in single cells at scale. The new procedure provides researchers with a tool for studying the epigenome and gene regulation in complex tissues and disease pathogenesis.

Using designed ankyrin repeat proteins (DARPins) technology, we discovered an α-helical conformation of the third variable (V3) loop on the human immunodeficiency virus 1 (HIV-1) envelope glycoprotein that renders the virus susceptible to broad neutralization at an intermediate entry stage after binding the CD4 receptor. Our results highlight the potential of post-attachment neutralization and enable exploitation of this helical region for inhibitor and vaccine design.

We engineered a tagged version of the yeast Rad51 recombinase and used this tool to monitor DNA double-strand break repair in living cells. We could observe how a broken DNA fragment can scout the nucleus to identify a similar sequence and use it as a template for repair.

By studying the folding of chromosomes relative to nuclear bodies in single-cell models, we reveal specialized subnuclear microenvironments linked to specific gene functions. Our models provide insights into a variety of structural features of the genome and unveil key structure–function correlations.

Inactivation of one of the two female X chromosomes involves condensing it into a repressive subnuclear territory, which is depleted of transcriptional components and undergoes late-stage DNA replication. Two new studies unravel how compartmentalization of the inactive mammalian X chromosome affects transcription and DNA replication.

Pioneer transcription factors access gene regulatory sites embedded within chromatin. They drive gene expression programs vital for cell fate decisions and cellular reprogramming, but how they engage nucleosomal sites at the molecular level is unclear. New results show that they engage histones and collaborate to overcome the nucleosome barrier.

NuA4 is a highly conserved histone acetyltransferase complex that functions in transcription and DNA repair. Four groups have recently determined the structure of NuA4 from two different yeasts using cryo-EM, revealing important mechanistic details of its function and allowing a detailed comparison to the related SAGA complex.

mRNAs that encode insulin in humans, mice, salmon and the fly Drosophila melanogaster are marked by methylated adenosines in the 3′ untranslated region (UTR). In D. melanogaster, these methylated adenosines are necessary for robust translation of the insulin mRNA into protein. In their absence, flies cannot regulate energy homeostasis and develop diabetes-like hallmarks.

Unlike autosomal genes, X-linked genes are expressed from only one copy in both male and female mammals. How cells increase X-linked gene expression to match autosomal levels is unclear. New evidence suggests that lower levels of RNA modifications on X chromosome-derived transcripts critically regulate mRNA stability and help to balance X-to-autosome gene expression levels.

Genome-scale CRISPR–Cas9 screens have identified genetic backgrounds that are vulnerable to inhibition of the SUMO modification pathway in human cells. These findings reveal that protein SUMOylation is essential for cell proliferation owing to a key role in complementary catenane resolution pathways that operate in interphase and mitosis to resolve intertwined DNA structures.

Immunoglobulin M (IgM) is the most ancient antibody class and key mediator of the primary immune response. New structures reveal how it binds to its only class-specific receptor (FcμR) and offer a tantalizing clue to the role of FcμR in the IgM B cell receptor.

The activity of genes is controlled by regulatory DNA sequences, which interact and communicate with their target genes over long genomic distances. New analyses show that the Mediator complex contributes to the formation of these long-range interactions in the genome.

A study on a yeast model explores how ssDNA gaps induce cell death and genomic instability, implicating Rad9 and Rad51 in gap repair and protection. Gaps forming secondary structures trigger chromosome fragility, deletions, rearrangements, or cell death pathways, showing how gaps are a vulnerability in cancer cells with opportunity for selective targeting.

Two new structural studies of the GABA transporter subtype GAT1 reveal detailed snapshots of the GABA transport cycle, providing new mechanistic insights and blueprints for rational design of novel leads that target GABAergic systems.

In this Review, the authors present and discuss the mechanistic and functional implications of new cryo-EM structures of telomerase from different species, contextualizing the new insights in light of existing functional analyses and decades-long hypotheses and conundrums.