The A1 domain is a component of the tubule and links helical repeats. (A) Cryo-EM map of the dimer-derived VWF tubule in gray with A1 domains in pink. A single A1 domain is boxed together with the domains of the neighboring molecules with which it interacts. (B) Details of the trans interactions an A1 domain makes with 2 neighboring VWF molecules. Distinct molecules are denoted by no apostrophe, 1 apostrophe (’), or 2 apostrophes (’’). (C) Quantification of tubule length observed by negative-stain electron microscopy with and without the A1 domain. Particle lengths were measured from 3 micrographs from samples incubated together overnight. Whisker plots are as described in the Figure 1E legend.