FIG. 7.

Targeting secretory vesicles: some current ideas. a. Saccharomyces cerevisiae: vesicles delivered to marked site on actin cables. (After Pruyne and Bretsher [131], with permission of the publisher.) b. Schizosaccharomyces pombe: vesicles delivered on actin cables to apical sites, marked by proteins carried on microtubules. c. Fungal hyphae: vesicles delivered on microtubules to a Spitzenkörper, from which they proceed to the apex, perhaps via actin filaments. d. Silvetia compressa (previously known as Pelvetia compressa): a current of calcium ions localizes the site of outgrowth, to which secretory vesicles travel on actin cables. e. Lily pollen tube: currents of calcium ions and protons into the tip localize the site of exocytosis; actin involved in this and in vesicle transport.