Fig. 7. Effect of Stx1-B subunit on the polymerization of actin and tubulin in ACHN cells. (A) ACHN cells were treated with and without 5 µg/ml of the Stx1-B subunit as described in Fig. 1 and lysed in the actin stabilization buffer. After removing aliquots from each whole lysate for the determination of total actin, polymerized actin (filamentous actin) was separated from soluble actin (monomer actin) by centrifugation. Both fractions of polymerized actin (pellet, upper panel) and total actin (whole, mid panel) were detected by immunoblot analysis and quantitated by densitometry. The proportion (%) polymerized was calculated by dividing the actin in the pellet fraction by the actin in the whole lysate and indicated (lower panel). (B) Tubulin polymerization was examined as in A.