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Approximately one-third of the Earth’s photosynthetic CO 2 assimilation occurs in a pyrenoid, an organelle containing the CO 2 -fixing enzyme Rubisco. How constituent proteins are recruited to the pyrenoid and how the organelle’s subcompartments—membrane tubules, a surrounding phase-separated Rubisco matrix, and a peripheral starch sheath—are held together is unknown. Using the model alga Chlamydomonas reinhardtii , we found that pyrenoid proteins share a sequence motif. We show that the motif is necessary and sufficient to target proteins to the pyrenoid and that the motif binds to Rubisco, suggesting a mechanism for targeting. The presence of the Rubisco-binding motif on proteins that localize to the tubules and on proteins that localize to the matrix–starch sheath interface suggests that the motif holds the pyrenoid’s three subcompartments together. Our findings advance our understanding of pyrenoid biogenesis and illustrate how a single protein motif can underlie the architecture of a complex multilayered phase-separated organelle. 

A circular economy (CE) would reduce both extraction and disposal by encouraging green design and circular business models, as well as repair, reuse, remanufacturing, and recycling. The CE started among architects and engineers, with little interest among economists. This article introduces CE concepts to economists, introduces key insights about the CE from other disciplines, and describes how economists can use these insights for a more complete economic analysis of policies that can better improve human welfare. An economic model of CE behavior can benefit from understanding the environmental gains from green designs based on engineering,transaction-cost savings from information based on blockchain technology, life cycle assessments based on industrial ecology, and behavioral science concepts of cultural barriers and social decision making that affect how producers and consumers respond to incentives. With various disciplines brought to bear on the subject, the combined analysis can exceed the sum of its parts.