Slow Diffusion of Proteins in the Yeast Plasma Membrane Allows Polarity to Be Maintained by Endocytic Cycling

VALDEZ TAUBAS J; PELHAM HR

CURRENT BIOLOGY

CELL PRESS

Año: 2003 vol. 13 p. 1636 - 1640

0960-9822

Yeast cells and the mating intermediates termed schmoos show a polarised distribution of some plasma membrane proteins.  Maintenance of this polarity is not well understood.  Here we show that the exocytic SNARE Snc1, which normally recycles between plasma membrane, endosomes and the Golgi, is polarised on the surface of both normal cells and schmoos, and that this requires its endocytosis.  Endocytic cycling, together with localised exocytosis, is sufficient to generate polarity because the rate of diffusion of Snc1 and other proteins in the yeast plasma membrane is very much slower than would be expected from measurements in animal cells.  Slow diffusion is a property of the plasma membrane: it is not observed on vacuolar membranes, and does not require the cell wall or polymerised actin, but is partially affected in an erg6 mutant defective in ergosterol synthesis.  An alternative model for schmoo polarity has recently been proposed in which protein localisation is driven by an asymmetric distribution of ergosterol-containing lipid rafts.  We have reinvestigated this, and conclude that neither the location of a GPI-linked marker protein nor filipin staining provides evidence to support such a model.  In contrast, endocytic cycling provides a simple and flexible mechanism for polarity maintenance.