The cover shows an artist’s impression of a cancerous cell in which DNA has formed micronuclei as a result of chromosomal instability. As Samuel Bakhoum and his colleagues reveal in this issue, when these micronuclei rupture, they spill exposed DNA into the cytosol (green), which prompts an inflammatory response that helps to drive metastasis. These findings draw a direct link between chromosomal instability and metastasis and may offer novel avenues for prevention. Cover image: Wenjing Wu

The cover is a surface—ribbon hybrid image showing the topology of the RNA Pol III/TFIIIB/DNA complex. RNA polymerase III (Pol III) catalyses the transcription of short RNAs that are essential for protein synthesis during cell growth. Pol III is predominantly regulated at the level of transcription initiation, and dysregulated Pol III activity is linked to diseases including cancer. In this issue, two independent studies from the labs of Alessandro Vannini and Christoph Mãƒâller describe cryo-electron microscopy structures of the yeast Pol III pre-initiation complex (PIC) comprising the full 17-subunit Pol III and the three TFIIIB subunits TBP (pink), Brf1 (yellow) and Bdp1 (orange) bound to promoter DNA in various functional states (the loops stabilizing the unwound DNA strands at both sides of the cleft are depicted as bright cyan ribbons). The structures elucidate the detailed mechanisms of how Pol III is recruited to its target promoters and how promoter DNA is opened to form a stable transcription bubble. They also allow a comparison with the structures of Pol I and Pol II PICs. Cover image: Alessandro Vannini/Jeroen Claus (Phospho Biomedical Animation)

The cover shows the William E. Gordon Telescope at the Arecibo Observatory in Puerto Rico. Jason Hessels and his colleagues used the telescope in their attempt to clarify the physical nature of the only known source of repeating fast radio bursts. Lasting about a millisecond each, these bursts come from a star-forming region in a dwarf galaxy. Hessels and his co-authors observed that the bursts were nearly 100% linearly polarized and had a very high Faraday rotation measure. Such results require the presence of an environment of extreme magnetized plasma, which has previously been seen only around massive black holes. As a result, the authors suggest that the radio bursts possibly come from a neutron star in such an environment (although the team notes that, in principle, the bursts could originate from a neutron star surrounded by either a highly magnetized wind nebula or a supernova remnant). Image: Image design: Danielle Futselaar; Photo usage: Brian P. Irwin/Dennis van de Water/Shutterstock.com

The ability to monitor microbial populations within the gut and other body organs poses significant challenges. In this issue, Mikhail Shapiro and his colleagues tackle this problem and reveal a technique that allows bacteria to be imaged deep inside the body using ultrasound. To achieve this, the team created genetically modified bacteria that express acoustic reporter genes. These genes encode components of gas vesicles — gas-filled nanostructures normally used by water-dwelling photosynthetic organisms to control their buoyancy. These gas vesicles scatter sound waves and so can be detected by ultrasound. The researchers show that populations of modified Escherichia coli and Salmonella typhimurium can be imaged non-invasively within the gastrointestinal tract and in tumours, offering a potential route for studying the microbiome and monitoring cancer progression and therapy. Image: Barth van Rossum for Caltech