Abstract
Cryptochrome (CRY) photoreceptors undergo photoresponsive homo-oligomerization to become physiologically active, and BICs (blue-light inhibitors of CRYs) suppress homo-oligomerization. Structural elucidation of CRY–CRY homo-oligomers and a CRY–BIC heterodimer reveals how the activity of plant CRYs is regulated by alternative protein–protein interactions.