Published online
doi:10.1083/jcb.200708060
The Journal of Cell Biology, Vol. 180, No. 6, 1219-1232
The Rockefeller University Press, 0021-9525 $30.00
© Idrissi et al.
Distinct acto/myosin-I structures associate with endocytic profiles at the plasma membrane
Fatima-Zahra Idrissi1,
Helga Grötsch1,
Isabel M. Fernández-Golbano1,
Cristina Presciatto-Baschong2,
Howard Riezman3, and
María-Isabel Geli1
1 Instituto de Biología Molecular de Barcelona, Consejo Superior de Investigaciones Científicas, 08028 Barcelona, Spain
2 Biozentrum, University of Basel, CH-4056 Basel, Switzerland
3 University of Geneva, CH-1211 Geneva, Switzerland
Correspondence to María-Isabel Geli: mgfbmc{at}ibmb.csic.es
Endocytosis in yeast requires actin and clathrin. Live cell imaging has previously shown that massive actin polymerization occurs concomitant with a slow 200-nm inward movement of the endocytic coat (Kaksonen, M., Y. Sun, and D.G. Drubin. 2003. Cell. 115:475–487). However, the nature of the primary endocytic profile in yeast and how clathrin and actin cooperate to generate an endocytic vesicle is unknown. In this study, we analyze the distribution of nine different proteins involved in endocytic uptake along plasma membrane invaginations using immunoelectron microscopy. We find that the primary endocytic profiles are tubular invaginations of up to 50 nm in diameter and 180 nm in length, which accumulate the endocytic coat components at the tip. Interestingly, significant actin labeling is only observed on invaginations longer than 50 nm, suggesting that initial membrane bending occurs before initiation of the slow inward movement. We also find that in the longest profiles, actin and the myosin-I Myo5p form two distinct structures that might be implicated in vesicle fission.
Abbreviations used in this paper: GDIT, gold distance to invagination tip; GDLB, gold distance to lipid bilayer; GDPM, gold distance to plasma membrane; GRP, gold relative position; IL, invagination length; WASP, Wiskott-Aldrich syndrome protein.

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