Volume 539 Number 7630

Editorials

News

News Features

The sparrow with four sexes p.482

Elaina Tuttle spent her life trying to understand the bizarre chromosome evolution of a common bird — until tragedy struck.

doi: 10.1038/539482a

News & Views

Clamping down on copy errors p.498

Repair enzymes must communicate across hundreds of nucleotides to undo errors made during DNA replication. Imaging reveals that the enzymes do this by forming a series of ring-like clamps that diffuse along the DNA. See Letter p.583

doi: 10.1038/nature20475

Polymers make charge flow easy p.499

Organic semiconductor devices require good electrical contacts with conducting materials, but such contacts are often inefficient. An approach that tackles this problem will enable a wide range of applications. See Letter p.536

doi: 10.1038/539499a

Insect invasions and natural selection p.500

Observations of a real-time invasion of Australia by Asian honeybees demonstrate how natural selection can allow a small founding population to overcome the genetic odds stacked against success.

doi: 10.1038/nature20472

Flexible graphene strengthens friction p.502

Previous observations showed that friction on graphene increases gradually when a probe starts to slide across the material's surface. Simulations now reveal that this effect is related to bending of the graphene sheet. See Letter p.541

doi: 10.1038/539502a

A mitochondrial brake on vascular repair p.503

Injured blood vessels are repaired by vascular smooth-muscle cells. It emerges that the protein Fat1 regulates the proliferation of these cells by inhibiting the function of mitochondria. See Letter p.575

doi: 10.1038/nature20476

Improving the image of nanoparticles p.505

A biocompatible probe that combines fluorescent nanodiamonds and gold nanoparticles allows cells to be imaged using both optical and electron microscopy techniques, opening up fresh opportunities for biological research.

doi: 10.1038/nature20478

A war over water when bacteria invade leaves p.506

Plants and bacteria battle for control of water during leaf infection, as is demonstrated by a bacterial species that manipulates plant cells to create a water-rich environment that promotes bacterial growth. See Article p. 524

doi: 10.1038/539506a

Review

Articles

Letters

Catalytic activation of carbon–carbon bonds in cyclopentanones p.546

In the chemical industry, it is often necessary to activate carbon–carbon bonds in order to synthesize complex organic molecules, but this is challenging when starting with simple five- or six-membered carbon rings; a new method uses a rhodium pre-catalyst and an amino-pyridine co-catalyst, enabling an overall energetically favourable reaction that involves activation of carbon–carbon bonds plus activation of carbon–hydrogen bonds.

doi: 10.1038/nature19849

A cannabinoid link between mitochondria and memory p.555

Cannabinoids affect CB1 receptors on the mitochondrial membranes in the brain, triggering a decrease in downstream cAMP-dependent signalling; this leads to a decrease in brain mitochondrial activity and to cannabinoid-induced amnesia.

doi: 10.1038/nature20127

Mechanism of super-assembly of respiratory complexes III and IV p.579

SCAF1 is always required for the interaction between the respiratory chain complexes III and IV, and in animals carrying only the short isoform of SCAF1, the respirasome is absent in most tissues, with the exception of heart and skeletal muscle, where COX7A2 is present instead of SCAF1.

doi: 10.1038/nature20157

Genetic and mechanistic diversity of piRNA 3′-end formation p.588

Small regulatory RNAs guide Argonaute (Ago) proteins in a sequence-specific manner to their targets and therefore have important roles in eukaryotic gene silencing. Of the three small RNA classes, microRNAs and short interfering RNAs are processed from double-stranded precursors into defined 21- to 23-mers by Dicer, an endoribonuclease with intrinsic ruler function. PIWI-interacting RNAs (piRNAs)—the 22–30-nt-long guides for PIWI-clade Ago proteins that silence transposons in animal gonads—are generated independently of Dicer from single-stranded precursors. piRNA 5′ ends are defined either by Zucchini, the Drosophila homologue of mitoPLD—a mitochondria-anchored endonuclease, or by piRNA-guided target cleavage. Formation of piRNA 3′ ends is poorly understood. Here we report that two genetically and mechanistically distinct pathways generate piRNA 3′ ends in Drosophila. The initiating nucleases are either Zucchini or the PIWI-clade proteins Aubergine (Aub) or Ago3. While Zucchini-mediated cleavages directly define mature piRNA 3′ ends, Aub/Ago3-mediated cleavages liberate pre-piRNAs that require extensive resection by the 3′-to-5′ exoribonuclease Nibbler (Drosophila homologue of Mut-7). The relative activity of these two pathways dictates the extent to which piRNAs are directed to cytoplasmic or nuclear PIWI-clade proteins and thereby sets the balance between post-transcriptional and transcriptional silencing. Notably, loss of both Zucchini and Nibbler reveals a minimal, Argonaute-driven small RNA biogenesis pathway in which piRNA 5′ and 3′ ends are directly produced by closely spaced Aub/Ago3-mediated cleavage events. Our data reveal a coherent model for piRNA biogenesis, and should aid the mechanistic dissection of the processes that govern piRNA 3′-end formation.

doi: 10.1038/nature20162