The Christmas wreath on the cover is a structural model of the repeat-containing domains of the Rpn1 and Rpn2 proteins that represent the largest subunits of the 26 S proteasome. The models have a novel protein architecture resembling an -helical toroid. The toroids have a central pore that would allow passage of an unfolded protein substrate through it. For details see the article by Kajava, pages 49791-49798.