We have addressed the function of the clathrin light chain Clc1+p in vesicle trafficking and morphogenesis in Schizosaccharomyces pombe. We show here that deletion of clc1 is lethal and that this lethality is remedied by osmotic stabilization. When grown in sorbitol-supplemented medium, clc1Δ cells present a reduction in acid phosphatase secretion, a delay in FM4-64 internalization, and fragmented vacuoles. These cells have a reduced β(1,3)glucan synthesis and defects in morphology, including loss of polarity and abnormal septa. Finally, clc1Δ cells have a strong defect in cell fusion and sporulation. Using a conditional mutant that allows modulating the amount of Clc1p, we have addressed the sensitivity of different cellular processes to a reduction in this protein. Thus, secretion of the Eng1 glucanase is more sensitive than secretion of acid phosphatase, and uptake of Lucifer yellow (pinocytosis) is more clathrin-dependent than uptake of FM4-64 (fluid phase endocytosis). This system has allowed knowing that actin patches, cables and contractile ring are altered when clathrin is reduced to 50%, while microtubules are not. Finally, the localization the β(1,3)glucan synthases Bgs1p and Bgs4p is more dependent on Clc1p than that of Bgsp, suggesting that vesicle transport of these enzymes could be differentially regulated.

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