The beta3A protein is expressed at very low/undetectable levels in platelets, macrophages and other tissues of pearl mice. Extracts (40 μg protein) from indicated tissues of mutant pearl mice and control C57BL/6J mice were analyzed by Western blotting. Sizes of MW standard proteins are indicated at right. Blots were reprobed with antibody to mouse actin (below) as a loading control. The high MW material observed near the gel origin in this experiment in macrophage extracts of normal and pearl mice was not reproducible.