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<jats:p>Chinstrap penguins fall asleep thousands of times per day in the wild</jats:p>

<jats:p>A large planet orbiting a very low-mass star challenges theories of planet formation</jats:p>

<jats:p>A volcanic island off the coast of Iceland celebrates six decades as a living laboratory</jats:p>

<jats:p>A vibrant history traces the triumphs and missteps of quantum, nuclear, and particle physics</jats:p>

<jats:p>Editors’ selections from the current scientific literature</jats:p>

<jats:p>Microsleeps, the seconds-long interruptions of wakefulness by eye closure and sleep-related brain activity, are dangerous when driving and might be too short to provide the restorative functions of sleep. If microsleeps do fulfill sleep functions, then animals faced with a continuous need for vigilance might resort to this sleep strategy. We investigated electroencephalographically defined sleep in wild chinstrap penguins, at sea and while nesting in Antarctica, constantly exposed to an egg predator and aggression from other penguins. The penguins nodded off &gt;10,000 times per day, engaging in bouts of bihemispheric and unihemispheric slow-wave sleep lasting on average only 4 seconds, but resulting in the accumulation of &gt;11 hours of sleep for each hemisphere. The investment in microsleeps by successfully breeding penguins suggests that the benefits of sleep can accrue incrementally.</jats:p>

<jats:p> Prokaryotic type III CRISPR-Cas antiviral systems employ cyclic oligoadenylate (cA <jats:sub>n</jats:sub> ) signaling to activate a diverse range of auxiliary proteins that reinforce the CRISPR-Cas defense. Here we characterize a class of cA <jats:sub>n</jats:sub> -dependent effector proteins named CRISPR-Cas-associated messenger RNA (mRNA) interferase 1 (Cami1) consisting of a CRISPR-associated Rossmann fold sensor domain fused to winged helix-turn-helix and a RelE-family mRNA interferase domain. Upon activation by cyclic tetra-adenylate (cA <jats:sub>4</jats:sub> ), Cami1 cleaves mRNA exposed at the ribosomal A-site thereby depleting mRNA and leading to cell growth arrest. The structures of apo-Cami1 and the ribosome-bound Cami1-cA <jats:sub>4</jats:sub> complex delineate the conformational changes that lead to Cami1 activation and the mechanism of Cami1 binding to a bacterial ribosome, revealing unexpected parallels with eukaryotic ribosome-inactivating proteins. </jats:p>