The regulation of cell wall synthesis by the clathrin light chain has been addressed. Schizosaccharomyces pombe clc1D mutant was inviable in the absence of osmotic stabilization; when grown in sorbitol-supplemented medium clc1D cellsgrew slowly, formed aggregates, and had strong defects in morphology. Additionally, clc1D cells exhibited an altered cell wall composition. A mutant that allowed modulating the amount of Clc1p was created to analyze in more detail the dependence of cell wall synthesis on clathrin. A 40% reduction in the amount of Clc1p did not affect acid phosphatase secretion and bulk lipid internalization. Under these conditions, b(1,3)glucan synthase activity and cell wall synthesis were reduced. Also, the delivery of glucan synthases to the cell surface, and the secretion of the Eng1p glucanase were defective. These results suggest that the defects in the cell wall observed in the conditional mutant were due to a defective secretion of enzymes involved in the synthesis/remodelling of this structure, rather than to their endocytosis. Our results show that a reduction in the amount of clathrin that has minor effects on general vesicle trafficking has a strong impact on cell wall synthesis, and suggest that this is the reason for the lethality of clc1D cells in the absence of osmotic stabilization.

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